Focusing Leica: Merklinger Method

Recently there are a few threads about technique in focusing Leica camera, such as focus at hyperfocal point etc.
Let me introduce Harold Merklinger's method of focusing.
In his opionion, the common practice of focusing at hyperfocal point is actually not as good as simply set the lens at infinity.
He wrote a lengthy technical book "The INs and OUTs of FOCUS" about his technique.
Harold Merkinger used Leica M3 with 50mm dual range Summicron for many of the illustrations in the book
For an introduction to his focusing method, see Harold Merklinger Focusing Method
For scenic photos, I usually set my Leica/Rollei/Minox camera to infinity and shoot.

 

I do mostly scenics and landscapes with Hasselblad, Leica R and M.
When the subject foreground and background are both at infinity, I
set the lens at infinity. When attempting to show acceptible
sharpness in foreground detail as well as at infinity, focusing at
infinity will work only if the lens/aperture chosen is such that
the "near end" of the DOF scale for that aperture encompases the
nearest point you want to appear acceptibly sharp. That would,
depending on focal length, closeness of foreground objects and film
speed, require increasingly small apertures and longer shutter times,
opening the door to diffraction degradation and image blur from
subject motion (i.e. things blowing in the breeze). Although
technically, you achieve true sharpness at infinity *only* if focused
on infinity (that goes for any subject at any distance), hyperfocal
is the only way to get *acceptible* sharpness over a range of
distances from near to infinity. Anyone who does a lot of that type
of shooting eventually recognizes the advantage of using equipment
that makes use of the Scheimpflug Principle as well, eg. large-
format, the Hassy flex- or arc-body or the Canon or Nikon Tilt/Shift
lenses.

 

It seems that H.M. may have shown that focusing on infinity can be
adequate in some cases, but I don't think he said anything that
argues in favor of this practice over hyperfocal distance focusing.
I don't usually settle for adequate; I usually want the best I can
get. Let's remember that D.O.F. is really just a euphemism for
acceptable unsharpness. In my view no unsharpness is acceptable
unless it's the best I can get.

 

Apprently, HM's method is seldom practiced here. Harold Merklinger's book is written with a lot of mathematics, not every one can follow his reasoning.
But instead of simply dismiss it, I urge all of you take one or two rolls of film and set it at infinity, and set the distance to one third of the focal length of you lens and shoot, you will be surprized at the result you get, and learn a valuable technique.
<p> For example if you use a 50mm Summicron, set apertue at 50/3 ~ f16, if you use a 35mm Summilux, set aperture at 35/3 or about f11 etc.
<p> Merklinger's method is based on DISK OF CONFUSION of the OBJECT FIELD, instead of circle of confusion in film plane.
When a lens is focus at infinity, the DISK OF CONFUSION is exactly equals to the lens open, for example if you set 50mm lens at f12, the diameter of the opening is about 4 mm, and the DISK OF CONFUISON is 4 mm. What does it means ? It means, ANYTTHING which is greater or equals to 4mm diamter will be RESOLVED. This cannot be said with hyperfocal distance focusing. When you focus a lens a hyperfocal , at 2x hyperfocal, the DISK OF CONFUSION = lens opening, but beyond 2x hyperfocal, the DISK OF CONFUSION increases without bound !
You must try it to believe it.

 

Harold Merklinger is a master is the theory of depth of field. This is not only manifested in his theory of Object field dof theory, but also in
hia masterful book on DOF theory for the view camera : Focusing the View Camera.
Scheimpflug principle is well know to LF photographers, but less the 0.1% of LF practisionner knows that Scheimflug principle is NOT ENOUGH, a long forgotten Second Scheimpflug principle-- the HINGE rule is necessary
to determine the focus of LF camera.
<p> Further, really only a handful of LF users know that the DOF in LF is RATICALLY different then that in 35mm camera.
in that the plane of near limit, exact focus and far limit are not parallel as in 35mm camera, but are three planes intersecting on the HINGE LINE, with the plane of exact focus at center, the far limit and near limit plane on both sides foring a wedge shape zone of aceptable sharpness extends to infintiy.
<p> For LF, only ths simplest case of low flowers on the foreground then mountain at distance is easy to encompass with lens tilt/back tilt. If you have a daisy in foreground, a cherry three at 10 meters, followed by a barn at 50 meters, then these three objects are not in a plane, then the handling of DOF is quite complicated.
HM is the only author I know of completely solved this problem with a set of tables in FOCUSING THE VIEW CAMERA. Any LF users will also benifit greatly from his books.

 

The failure of conventional hyperfocusing method was masterfully demonstrated by Merlinger with as set of 5 photographs on page 23 of The INs and OUTs of FOCUS: He photographed his niece June with a 50mm/F2 dual range Summcron at F8, focusing on hyerfocal distance 9.1m; June was standing at 3m, 4.6m, 9.1m, 18.3m and 49m, at corresponding distance, holding one card bearing 3, 4.6, etc at corresponding distance to show at what distance the picture was taken.
Among the five pictures, only the ones at 3m, 4.6m 9.1m and 18.3 m were sharp, while the June the persona the the card at 49m was COMPLETELY BLURRED. The traditional hyperfocusng method can only deliver depth of field up to 18.3 m, it failed completely at 49m.
<p> As a stark contrast, Harold Merklinger demostrated the powerful result of his INIFINITY focusing method. In a secons set of 5 photographs in page 30, Merkonger again photographed June, with same 50mm/F2 Summcron, at same F8, but this time, FOCUSED AT INFINITY.
At 1m, 3m,25m 50m and 100m. The pictures at 3, 25m were sharp, at 50mm, the "50" on June's hand held card is clear, and even at 100m, the letters "100" on June's card were still decernable (albeit rather blurry, but still far better than the picture at 49m of previous tests when the lens was focused at hyperfocal distance 9.1m )
Conclusion: Summicron 50mm/F2 aperture F8 focused at hyperfocal distance 9.1m is really sharp from 3m to 18.3, beyond that it fails.
<p> On the contrary, same Summicron, same F8, but FOCUSED at INFINITY: The pictures were sharp from 1m to 50m and beyond. <p>
In other words. Merklinger's infinity focusing method actually delivers a much depth DOF then conventional method !

 

I strongly recommend BUY the book The INs and OUTs of FOCUS. A great deal of material, including the two sets of tests, Hyperfocusing vs Infinity focusing pictures of June were not posted on his website.
<p> This book is a must have for any Leica camera user. What is the point of possesing the best lenses in the world, but fail to use it to maximum power ?
<p> This book is far more important then buying another expensive Leica lens to your holdings.
<p> Harold Merklinger provides a road map for Leica lens users how to get the best out of their lenses !
<p> Of course his method is equally applicable to other brands of lenses.

 

Harold Merlinger, as a LF user, loves landscape photography. He was disappointed with the traditional focus at hyerfocal distance mehod, and tried different methods, including smaller apertures, but still not satisfacotry. He then took on himself to seriously investigate the matter, he searched literature on DOF theories as far back as 1933 article on depth of field by Vith in Leica Handbook, Rudolf Kingslake :The Complete Photographer 1942, and G. H Cook (of Taylor Taylor and Hobson ) 1950 Leica Photography articles, followed up with intensive
experimetation and mathematical deductions. He finally worked out a completely new theory of DOF.
<p> He wrote: Since working out these details, I find I do a lot of photography with the lens simply focused at infinity.

 

Leicaphile Merklinger's method is really SIMPLE:
<P> 1) Focus at infinity <p> 2) How to select aperture ? Ask yourself, what is the smallest object you want it to be resolved ?
the look at your lens, turn the aperture ring, close down the aperture to THAT size. That is it.

 

Dr. Merklinger is also a camera collector, he had written articles on camera and lens on Shutterbug.
I remember one of his camera collector corner article was about dual range Summicron lens

 

Is there something wrong with focusing on the subject of the picture?
When people start discussing various shortcuts to use to turn multi-
thousand dollar instruments into $10 plastic throw-away type cameras
I cringe.

 

I tend to agree with Darnton. Too much hyperfocal distance setting is
bad for sharpness! For slides that are to be projected you really
notice the difference between objects that have been deliberatley
focussed on and those that are just within the depth of focus. When
viewing slides I think that hyperfocal distance methods are not so
effective. For prints this is often not the case. However, I still,
even in 6 x 6, try and ensure that I focus on the main point of
interest and try and get the DOF to include the other items I feel
need to be sharp rather than adjust the focus so that the DOF could be
adjusted to get all the objects "in focus" which thereby sacrifices
critical focus on the main object of interest.

 

See paragraph "depth of field problem"

<p>

http://www.geocities.com/Athens/Atlantis/4628/sharpness.html

 

Discussions at LUG

 

Why Focusing at Infinity Makes Sharper Landscape Picture

In landscape pictures, main subjects of interest are located 10 meters and stretch to infinity.
In the following two tables illustrate the difference in sharpness between focusing at hyperfocal point and focusing at infinity for objects 10 meters and beyond.

• Lens: Summicron R 35mm/F2 lens
• Aperture : f8
• Hyperfocal distance : 4.6 M
• Lens opening = 35mm/8= 0.44 CM

• TABLE 1
  • 
    At 2x 4.6 m, the disk of confusion = lens opening =4.4 mm;
  • 
    Beyond that, disk of confusion increases without bound.
  • 
    For example at 100 meter, the disk of confusion is 9 CM, meaning feature smaller than 9 cm will not be resolved.
  • 
    For instance, you will not be able to see people's eyes (about 2 cm) or mouth ( 5 to 6 cm ).
  • 
    Objects bigger 9 cm for example a hat will still be resolved at 100 M
  • 
    Circle of confusion INCREASES with distance, although still stays within the limit of 0.033 mm.
  TABLE 1: FOCUS AT HYPERFOCAL
  Distance M ​
  Circle of confusion mm ​
  Disk of confusion cm
  0.9 ​
  0.1500 ​
  0.36
  1 ​
  0.1200 ​
  0.34
  2.3 ​
  0.0300 ​
  0.22
  3 ​
  0.0200 ​
  0.16
  3.8 ​
  0.0070 ​
  0.08
  4 ​
  0.0050 ​
  0.06
  4.5 ​
  0.0010 ​
  0.01
  4.6 ​
  0.0000 ​
  0
  5 ​
  0.0020 ​
  0.04
  6 ​
  0.0080 ​
  0.13
  10 ​
  0.0180 ​
  0.51
  20 ​
  0.0260 ​
  1.45
  30 ​
  0.0280 ​
  2.4
  40 ​
  0.0290 ​
  3.34
  50 ​
  0.0300 ​
  4.29
  100 ​
  0.0320 ​
  9.01 ​
  TABLE 2
  The disk of confusion remains at 0.44 cm from 10 meter to infinity.
  By focusing at infinity, you will be able to resolve feature greater than 0.44 cm-- you can see people's eyes, camera straps etc 100 M away, not just hats.
  • 
    At 5 meter, , that is the near limit of depth of field, the circle of confusion is 0.03mm
  • 
    From 5 M and beyond, the circle of confusion DECREASES with distance, at 10 M coc= 0.015 mm, at 50 M coc= 0.003 mm at 100 M coc=0.0015 mm. You can see that these numbers are much smaller than the corresponding numbers of table 1
  • 
    Although the actual circle of confusion when focusing a lens at infinity is not as small as these numbers, due to diffraction effect but are still as small as the resolution of the lens permits.
  TABLE 2 FOCUS AT INFINITY
  Distance M ​
  Circle of confusion mm ​
  Disk of confusion cm
  1 ​
  0.16 ​
  0.44
  2 ​
  0.08 ​
  0.44
  5 ​
  0.03 ​
  0.44
  10 ​
  0.02 ​
  0.44
  20 ​
  0.008 ​
  0.44
  30 ​
  0.005 ​
  0.44
  50 ​
  0.003 ​
  0.44
  100 ​
  0.0015 ​
  0.44 ​

 

I definitely see the difference between zone focused snaps and spot
on focusing - especially with the new asphs. These lenses engrave the
in-focus contours so sharply into the emulsion that anything else is
just not as good. The beauty of the M is that focus is so positive.
Maybe no quicker, depending on your skill level, but you really
_know_ when something is in focus. That's why I continually refocus
like an obsessive.

<p>

Rob.

 

RE snap on focus
Absolutely, when you are photography a person's face, or a painting on a wall, you must focus on the spot.
But where do you focus your Leica such as

 

I must say that this has been an illuminating discussion for me.
I've been dutifully using my DOF scales and wondering why focus at
infinity was so bad in my landscapes. Now I know. Thanks for
sharing this, Martin.

 

re: snap on focus: On the sign, the only area of sensible data in the
brightest spot on the photo, to which the eye is ultimately drawn. If
you don't have some sort of center of interest in a photo, you're
better off not pushing the button.

 

Ed A few years ago, in rec.photo.medium+format news group, a photographer complained that he used his MF camera using according to the DOF rules for his landscape pictures, but when enlarged the distant objects were quite unsharp. Then I pointed to him Merklinger's book

a few weeks later he posted another message, saying his results were greatly improved.
IMO, this book is one of the best technical book about how to get sharp pictures with great depth of field.

 

Martin,

<p>

Thanks for all the info. It's really very inteteresting and helpful.
Some personal observations about my own results:

<p>

I hardly ever use my Leica equipment for the type of photography
requiring infinity focus, such as the typical landscape image. Most
of my Leica images are made at intimate distances at large apertures,
where precise focussing on a particular element is necessary, and the
maximum DOF is either not possible or not important. So I never
bothered too much with hyperfocal settings, and when I did I was only
concerned with the sharpness in the middle distances or at the
focussed point, not at infinity.

<p>

However, for a long time I was using the hyperfocal method of
focussing for landscape type images with my 38mm Zeiss Biogon, a lens
that I often used on a tripod at minimum apertures for maximum DOF and
sharpness. I was using the traditional hyperfocal settings when
stopping down to f/16 or f/22, hoping to get everything in sharp focus
from the immediate foreground to infinity.

<p>

I often found that the distant subjects at infinity were not
critically sharp, and unless I used an aperture one or two stops
smaller than my hyperfocal setting I would usually see a softness in
the distant backgrounds. Then I started focussing at infinity, even
when stopping down to f/16 or f/22, and was amazed at the incredible
difference in sharpness at infinity. And the foregrounds and middle
grounds were just as sharp as before, when I used the hyperfocal
settings.

<p>

Take care, Sergio.

 

It looks like there's som empirical evidence out there to support
this idea. It is difficult to understand why infinity should not be
included within the zone of acceptably (un)sharp focus, equally as
well as all other distances within that zone. The observation, which
seems pretty well true, that DOF extends about twice as far behind
the plane of focus as before it, suggests that the best point of
focus when DOF is desired, is at a distance relatively closer to the
camera than the midpoint bewteen the lens and the farthest subject of
interest. Ansel Adams wrote someplace that he thought it usually
best to focus on the nearer of two objects.

<p>

Nevertheless, the only scientific thing to do is to give it a try,
which I will do. I do agree that focusing on the subject of main
interest is a good idea, which has something to do with why that
rangefinder is provided!

 

I have found Merklinger's articles in the net a couple of years ago.
All the math is absolutely correct. During this years I used
sometimes his approach (and use it now when needed) and I confirm it
works fine. (Even though I don't have Leica; I hope the community
forgives me my SLR).

<p>

The important point is to undestand, that focusing on the infinity
does NOT give you "sharp" foreground (as sharp as it could be if you
focus on this foreground), but allows you easily evaluate the
unsharpness level and decide if this unsharpness is acceptable for
your purposes. But Martin has already pointed it out above.

<p>

Merklinger's method makes it also possible evaluate DOF when the
focus in not in the infinity. I do it also, it works great. The
unexpected problem was the relationship between the quantity (the
size to be resolved) and the quantity (what a given quantitative
unsharpness looks like). The articles give some examples, but
practice is necessary.

<p>

Merklinger's method makes possible to easily solve an opposite task:
make something intentionally blurred. We so often try to get maximum
sharpness and so often forget about the artistic effect of
unsharpness...

<p>

I have no Merklinger's book; in my opinion his articles in internet
contain all the neccessary information (even more detailed than
needed to comprehend the idea and to follow the math).

<p>

I want also attract attention to his article about bokeh ("Thechnical
view on bokeh"). As far as I know it is the first attempt of a
rational attack on this "mysterious" property.

<p>

Thanks and sorry for my bad English.

 

Sorry, a misspell: it should be
...between the quantity (the size to be resolved) and the QUALITY
(what a given quantitative unsharpness looks like). ...

 

Martin, thanks for very useful info. To demonstrate partly the
difference between Merklinger’s and hyperfocal method of focusing I
take the SLR camera (Nikon F, 1.4/50) and focus the lens on
hyperfocal distance 5m at f/16 stop. Then look at any subject at
infinity and stop down the aperture to f/16 with pre-set knob. It’s
very noticeable that the subject stays OUT of focus yet, but when
turning the lens ring to infinity mark, the subject becomes as sharp
as possible. You could also watch how the sharpness of images (from
1m to 50m and beyond) is changing when changing f/stop.

<p>

Regards

<p>

Victor

 

Better late than never?

It's been awhile since this thread was active, but hopefully some of the original posters will reply to this...

If the largest circles of confusion seen in the foreground, forward of the plane of sharpest focus, are "acceptable" (i.e. "small enough") when focused at infinity, would circles of this size not be found equally acceptable if they occurred in the background as well, when focused at some point short of infinity?

This would extend the range of acceptable sharpness, making use of the DoF that exists just beyond the plane of sharpest focus instead of wasting it the way Merklinger and his disciples do when focusing at Infinity.

In other words, if the circles on the near side of the plane of sharpest focus are acceptably small, why not use those of equal size that lie beyond the plane of sharpest focus?

I can't imagine anyone answering this satisfactorily. Focusing at infinity when any portion of the subject space resides at some distance short of infinity is a waste of useful DoF.

Mike Davis

http://www.accessz.com

 

Somehow, the text in this thread became centered. I have no idea how to fix that but it's annoying.

I was interested to read Martin's advice when this thread started but have been unable to contribute anything useful from my own experience. I envy those who can see anything at "infinity", such as the horizon. Here, in Jakarta and surrounding countryside, there is so much atmospheric haze that the horizon is usually invisible. In the city itself, even buildings less than a kilometer away appear as ghosts.

There are mountains to the south of the city but they can be seen only perhaps on three or four days each year, during the rainy season when there has been heavy rain and some wind the night before. (Pollution, which is severe, tends to accumulate because this is not a windy place; most days, you could blow smoke rings out of doors!)

 

Mike,
Merklinger suggest focusing at infinity as an ALTERNATIVE to hyperfocal focusing. The goal here is to get the resolution threshold=aperture hole diameter AT EVERY DISTANCE.

If your scene requires only a finite DOF, i.e. there is a near and a far plane (YOU want to get a required resol.threshold only between this two planes) then you should not have to focus at infinity. According the Merklinger approach you have to focus at a plane exactly between these near & far boundaries. And the needed aperture is given by Merklinger formulas.

An attempt to get rid of centering:
Success?
Or not?

 

Mike,
There is no magic in dof, there is aways that much dof to distribute, and there are two approaches

• Front end biased, foreground objects predomenat use traditiona DOF method
• Far end biased, when objects, scenes at distance are predominant then use Merklinger way, focus at infinity

• I think it is a matter of choice.
  If in a scene, the close up subject is predominant, then use the conventional DOF method.
  On the other hand, if in the scene there are more scene at distance then close by, then I use Merklinger method.
  I do a lot of Minox picture with Merklinger's focus at infinity method.

 

For example, Minox camera at wide open f/3.5 has diameter 15/3.5= 4.3 mm. When focus at infinty, any object in the scene with diameter>4.3mm will be resolved.
In the sample Minox picture, the diameter of the grids, and the spacing between the grids are all less then 4.3mm, hence they are sharp from front to rear
If the Minox was focus at hyperfocal distance of 2 M instead of at infinity, all the grids would not be solved from near to far, because the disk of confusion grows larger and larger.

 

Martin,

Thanks for sharing the nice photo, but using a Minox image to illustrate the acceptable DoF had when focused at infinity is like arm wrestling with Hulk Hogan to prove that bald men are stronger than those with a full head of hair.

The smaller the format the more DoF you get using equivalent focal lengths. Your use of f/3.5 also avoided the visible dffraction suffered by Minox cameras when stopped down.

You wrote, "there are two approaches" - "front end biased" and "far end biased" - stating that it's "a matter of choice." If you are knowingly "choosing" to secure softer foregrounds by focusing at infinity, fine, I will vigorously defend your choice, but if you believe your "choice" provides sharper images than can be had with the "conventional DoF method", you are mistaken.

You wrote, "If in a scene, the close up subject is predominant, then use the conventional DOF method."

Please explain what advantage focusing at Infinity offers over "the conventional DoF method" when "scenes at a distance are predominant."

There is no advantage.

You haven't answered my original question. Here it is again:

If the largest circles of confusion seen in the foreground, forward of the plane of sharpest focus, are "acceptable" (i.e. "small enough") when focused at infinity, would circles of this size not be found equally acceptable if they occurred in the background as well, when focused at some point short of infinity?

Yes or No?

Your "choice" to use Merlinger's method when the scene is predominantly at a distance clearly indicates that some portion of your subject falls short of infinity and you are enjoying at least some near-side DoF if you find the nearest subjects acceptably sharp. If that's the case, why are you choosing to waste the acceptably small, equal-diameter circles of confusion that lie beyond the plane of sharpest focus?

Merklinger's method is not an acceptable alternative to the conventional method if image clarity is our goal. Focusing at infinity and stopping down enough to get acceptable results at the nearest subject invites three sources of image degradation which you would not suffer were you to shoot at a wider aperture and focus more closely (yielding acceptably small CoC's at both the near sharp and at infinity):

1) Stopping down further than necessary increases the diameter of diffraction's Airy disks. (As circles of confusion shrink when stopping down, Airy disks get larger.)

2) Stopping down further than necessary increases your vulnerability to camera and subject motion because longer expoures must be employed.

3) Stopping down further than necessary may take you further away from the aperture at which your lens delivers its best resolution.

So, please tell me how it's advantageous to focus at infinity and then stop down enough to achieve acceptably small circles of confusion at the near sharp, when those same diameters could have been enjoyed at a wider aperture (at both the near sharp and at infinity) were you focused at the hyperfocal distance.

Most people are disappointed by "the conventional DoF method" because they are using DoF scales engraved on their lenses (or some other DoF reference) that were generated with too large a circle of confusion diameter for the enlargement factor and viewing distance their application requires. Many DoF calculators treat circle of confusion diameter as a constant that's unique to each format (0.03mm for 35mm, 0.06mm for 6x6cm, etc.) and the lens manufacturers' engravings are obviously inflexible - they only work for one ratio of viewing distance to enlargement factor (and are usually not very aggressive in the first place.)

Handling circle of confusion diameter as a constant when calculating DoF for a given format is ridiculous. It's a variable. Before you can calculate DoF you must calculate the CoC that's right for your application. Here's how:

Maximum Permissible CoC Diameter On-film = 1 / enlargement factor / desired print resolution

The average adult with healthy vision can resolve no more than 6 to 8 lp/mm at a distance of 10 inches. So, if you want a resolution of 7 lp/mm in your final print for an 8x enlargement factor, you must limit on-film circle of confusion diameters to:

Maximum Permissible CoC Diameter On-film = 1 / 8 / 7 = 0.0179 mm

(This is much smaller than the 0.03 mm value typically used to calculate DoF for the 35mm format.)

That's for a viewing distance of 10 inches. If, however, you intend to make a print that will be displayed such that it can be viewed no closer than 30 inches, instead of at 10 inches, you should reduce your resolution requirement by a factor of three:

Maximum Permissible CoC Diameter On-film = 1 / 8 / (7 / 3) = 0.0536 mm

(That's much larger than the 0.03mm value typically used for 35mm format.)

It's just that easy to come up with a value for CoC you can plug into your choice of several DoF calculators/spreadsheets/Palm programs/java scripts/whatever that actually permit you to specify the on-film maximum accpetable diameter for CoC's.

When coming up with the enlargment factor, don't neglect to take cropping into account. If, for example, you intend to make an 8x10 print from the 24x30mm portion of the fullframe 35mm negative, you'll want to calculate the enlargement factor using the smaller dimensions.

A little experimentation with tables generated using this approach will tell you by how many stops you have to offset the f-stops suggested by your lens barrel DoF scale for each lens. That way, no math is required in the field. You just have to do your homework up front.

At best, Merlinger's suggestion is a novel procedure that compromises image quality for the sake of convenience. It is not a reasonable alternative to the conventional method nor is there room for subjective input if image clairity is your goal. If you doubt my contention, revisit my original question and consider the pitfalls of stopping down unneccessarily.

Mike Davis
www.accessz.com

 

"If the largest circles of confusion seen in the foreground, forward of the plane of sharpest focus, are "acceptable" (i.e. "small enough") when focused at infinity, would circles of this size not be found equally acceptable if they occurred in the background as well, when focused at some point short of infinity?

Yes or No?"


-- Yes.


"Merklinger's method is not an acceptable alternative to the conventional method if image clarity is our goal."


If the "clarity"” is not compatible with resolution threshold at every distance = aperture diameter, then Merklinger's method is NOT an acceptable alternative. Otherwise it IS acceptable. --- It depends on your requirements.

"1) Stopping down further than necessary increases the diameter of diffraction's Airy disks."

Sure. Moreover it can be shown, that if we take into account the diffraction then there is no reason to focus beyond a certain point. But this point is much farther than usual hyperfocal distance. I don't like to post formulas into the forum, but it is not difficult.


"...when those same diameters could have been enjoyed at a wider aperture (at both the near sharp and at infinity) were you focused at the hyperfocal distance."


I beg to differ. I don't mind the "near sharp" but the resolution at infinity is much worse if we focus at hyperfocal distance compared with the case when we focus exactly at infinity (or, more precisely, at that far point I mentioned above). --- Generally speaking, it is not a surprise: anything is sharper when the focus is at it than when it is only kept within a DOF.


As an aside note.
Merklinger's approach is a special one (criterion is in terms of resolution threshold in space of objects), but it DOES relate to a classical approach (where criterion is in terms of circle of confusion in space of images). Indeed, lets generalize a bit the Merklinger's criterion: lets ask for different res.thresholds at near and at far limits of sharpness zone. The new formulae are easy to obtain. Then consider a special case when we require that the size of res.threshold is proportional to the distance. If you obtain the formulae for this case you will see that the formulas fully agree with simplified CLASSICAL DOF formulas (the simplification is for situations when focusing distance is significally greater than the focal length, -- it is ok for every situation except close ups). In other words, if we request the same ANGULAR resolution threshold at near and far limits of a scene, then Merklinger's result is totally identical with classical result.

 

Mike wrote:

"The smaller the format the more DoF you get using equivalent focal lengths. Your use of f/3.5 also avoided the visible dffraction suffered by Minox cameras when stopped down."<p>
Stop down Minox ? <p>
There is no such thing as stopped down with Minox 8x11 cameras. For
Minox A, B,C, LX, TLX, CLX, the lens is always used at wide open f/3.5. There is no aperture control<p>

"Please explain what advantage focusing at Infinity offers over "the conventional DoF method" when "scenes at a distance are predominant."

There is no advantage. "<p>
Sure there is, great advantage<p>

"If the largest circles of confusion seen in the foreground, forward of the plane of sharpest focus, are "acceptable" (i.e. "small enough") when focused at infinity, would circles of this size not be found equally acceptable if they occurred in the background as well, when focused at some point short of infinity?

Yes or No? " <p>
The answer is No.<p>
<p>Think for yourself for a moment, " What object corresponds to 0.03mm at far zone ?"
<p> For example, at 30 meter with 50mm lens, the magnification is
approximately 600 times, a 0.03mm corresponds to 18 mm.
<p> It is far to big. I prefer not using ONE coc for both far and near object, instead, I prefer a sliding scale of coc, ie, for distance
object, use very small coc (ie, 0.005 mm at 30 meter) and at the same time, for forground object use larger coc( 0.03 at 5 meter)
<p>That is what focusing at infinity offeres: a sliding coc, smaller
coc for far object, larger coc for near objects.

 

Martin,

I stand corrected regarding use of stops below f/3.5 with a Minox. I don't know where I heard that and have never used a Minox. Thanks for catching that one. Still, the DoF enjoyed by this small format makes it a poor choice for illustrating that sufficient DoF can be had when focused at Infinity.

As an aside: Minox's choice to fix the aperture at f/3.5 was a great idea considering the enlargement factors this format must endure.

The on-film Airy disk diameter at f/3.5 is 0.0047384mm.

3.5 * 0.00135383 = 0.0047384 mm

Given that the reciprocal of 7 lp/mm is 1/7 mm, or 0.1429 mm, this means that in regards to diffraction at least, the Minox negatives can tolerate a 30x enlargement before the Airy disks produced at f/3.5 would become visible in a print viewed at a distance of 10 inches.

0.1429 / 0.0047384 = 30.16

Thus, at f/3.5, you can enlarge the 8x11mm negatives to 9.5 x 13 inches without suffering visible diffraction (7 lp/mm).

Regarding your preference for a "sliding CoC" - "smaller coc for far object, larger coc for near objects":

If we share the goal of making both the near and far CoC's too small to resolve in the final print at the anticipated viewing distance, focusing closer to infinity or at infinity (such that the far CoC will be smaller than the near CoC) will require a smaller aperture than could be used if we instead focused at the hyperfocal distance. Your preference for making the far CoC's smaller than the near CoC's means that you either permit the near CoC's to be resolvable (visibly out-of-focus) in the foreground so that you can use the same or wider apertures than you would if focused at the hyperfocal distance -OR- you don't tolerate soft foregrounds and do make the near CoC's unresolvable by stopping down to compensate for having focused beyond the hyperfocal distance. Which is it?

Are you allowing foreground subjects to be visibly out of focus so that you can shoot at wider apertures or are you stopping down more than you have to keep the nears visibly sharp despite having focused too long? Neither of these possibilites are pallatable to me.

My original question spoke in terms of the near and far both being "acceptably" sharp (not resolvable in the final print) - your response implies that Infinity subjects can not be made acceptably sharp without focusing beyond the hyperfocal distance. That's incorrect. Independant of problems with diffraction (which I discussed above), for every situation, one can find an aperture at which the CoC's will be small enough at Infinity, when focused at the hyperfocal distance, to make both the near and Infinity coc's just sharp enough to be unresolvable by the human eye. This aperture will be wider (faster) than the aperture you would have to use to make your nears visibly sharp when focusing beyond the hyperfocal distance.

Merklinger's suggestion compromises foreground sharpness or speed - take your pick.

Mike Davis

 

Hi Andrey,

In response to my having written "...when those same diameters could have been enjoyed at a wider aperture (at both the near sharp and at infinity) were you focused at the hyperfocal distance."

You wrote: "I beg to differ. I don't mind the "near sharp" but the resolution at infinity is much worse if we focus at hyperfocal distance compared with the case when we focus exactly at infinity (or, more precisely, at that far point I mentioned above). --- Generally speaking, it is not a surprise: anything is sharper when the focus is at it than when it is only kept within a DOF."

Like Martin, your words imply that it is somehow impossible to find an aperture at which CoC's will be small enough to be unresolvable for both the near and Infinity when focused at the hyperfocal distance.

My second posting to this thread clearly explained how to select a CoC diameter for use in DoF calculations that will be unresolvable in the final print at the anticipated viewing distance. That diameter can be achieved simultaneously at both the near sharp and at Infinity ONLY when focused at the hyperfocal distance. At the aperture calculated in "conventional" DoF calculations using the appropriate CoC value, stopping down any further in an effort to make CoC's smaller still, would be pointless - you wouldn't be able to SEE any improvement in the final print. At THIS aperture, if we were to focus closer to Infinity than the hyperfocal distance, we would only make the foreground CoC's larger (visibly defocused) and the Infinity CoC's needlessly smaller than (they were already unresolvable when focused at the hyperfocal distance.) How can you "beg to differ" when I say that Merklinger's method would require stopping down to a smaller aperture than this one to re-establish unresolvable CoC's in the foreground?

Also: DoF is the range of distances in which subjects are found acceptably sharp in the final print at a given viewing distance. Your statement that "anything is sharper when the focus is at it than when it is only kept within a DOF" makes no sense in the context of the definition of DoF. The only way your comment could be deemed correct would be to modify the definition of DoF to read like this: "DoF is the range of distances in which subjects MAY OR MAY NOT be found acceptably sharp in the final print at a given viewing distance." In other words, DoF defines the range of distances where everything is "acceptably" sharp, so how could anything look sharper when the focus is biased toward one end of the range, when doing so would make subjects at the other end unacceptably sharp. You used the term "DoF" in your statement without honoring its meaning.

Mike Davis

 

"Sliding coc" eh? Maybe I should give the merklinger method a go...

 

smaller coc for far object, larger coc for near objects
We all know what that feels like, I'm sure...
OK, enough coc jokes. I promise.

 

There is one thing here that I do not understand, and thus do not agree with.

In describing Merklinger's tests, Martin Tai pointed out that focusing the lens at 9.1m, objects from 3m to 18.3 m were acceptably sharp. He then went on to say that by focusing at infinity, objects from 1m to 50 m and beyond were acceptably sharp. Now how can it be that focusing FURTHER AWAY will bring CLOSER objects to acceptable focus?

The only explanation I can come up with is that by focusing closer, you actually increase your focal length slightly , which should reduce your depth of field. But since the actual aperture stays the same, the relative f stop also decreases the same amount, and should compensate. (120mm lens at infinity, F8, actual aperture is 15mm. Focusing closer, say by 10mm, focal length is now 130mm, relative aperture F8.7). However, at normal shooting distances the difference is so small that it should not have an effect. And certainly not that big effect to bring objects from 1 m instead of 3m into sharp focus.

As I see it, there exists a depth of acceptable sharpness in front AND behind the plane of focus. Merklinger and Martin seem to agree that this field of acceptable sharpness occurs, at least in front of the plane of focus, at least when focused on infinity. Exactly how wide this field is depends on aperture and size of reproduction, as well as on how critical eye is used to judge the result, while using the same lens and film size. If we agree that this field of sharpness occurs in front of the plane of focus, I think we should also easily accept that it does also occur behind the plane of focus. In books it is commonly said that the depth of field actually extends one third in front of the plane of focus and two thirds behind it.

If this is true, and I really can't see any reason why it would not be, then by focusing at infinity you will lose that part of the depth of field that goes beyond infinity. And by focusing at a point closer than infinity, you would get a wider acceptable depth of field. That is, a closer object would be in acceptable focus than if you focused at infinity, while object at infinity would still be in acceptable focus.

Exactly where to focus and what aperture to use? Now that depends on the factors mentioned above, focal length, film size, size of reproduction and the viewing distance. Lens manufacturers use certain assumptions when engraving their depth of field scales. You must not accept them as given without testing that you agree with the assumptions! But that does not make the theory behind it invalid.

If your lens says hyperfocal distance focusing at 10m and aperture at f8 will bring everything from 5 m to infinity sharp, you may disagree with it and instead use 1-3 stops smaller aperture at same distance setting. To compensate for your higher requirements for what is acceptable sharpness.

 

Hi Mike,


"DoF is the range of distances in which subjects MAY OR MAY NOT be found acceptably sharp in the final print at a given viewing distance."


DoF is the range of distances in which subjects are found equally or more sharp than a minimum sharpness level required by the chosen criterion.


Your second posting to this thread is indeed very important to understand your logic. I admit I considered it only in positive sense, as a way to enhance the CoC standard, but there is also a negative sense there: any extra sharpness beyond the level of acceptable sharpness in an overkill and is either useless (invisible) or harmful (wasting of resources). Your predefined enlargement factor and viewing distance act as a cut off filter.


These restrictions are not perfect (a curious viewer can come closer, I may arrive at idea to make greater enlargement etc), but if we assume that we can guarantee that enlargement factor and viewing distance are always kept as intended, then I agree with your logic.


It can be shown that, when the focus in on hyperfocal distance, the linear resolution gets progressively worse after h.distance, and this degradation is unrestricted. On the other side, the angular resolution keeps constant. When the focus is at infinity, the linear resolution is constant, the angular resolution threshold is 0 (in realty we shouldn't ignore the diffraction in this case, but for sake of discussion we will).

The goal of focusing at infinity is to keep objects located at infinity as sharp as possible.

According your logic even if there is nothing in foreground (e.g. only distant mountains, moon and stars in the sky) it does not matter shall I focus at infinity, at hyperfocal distance or somewhere in between. You probably admit that in principle there will be difference in moon clarity, but that cut-off filter will destroy the difference and our canonical viewer will perceive all three versions as totally identical. --- Correct?

The same note for a scene without infinity, say from 3m to 5m. If our DoF does exactly cover this range, the extra sharpness gained at exact focus plane is useless: the canonical viewer won't appreciate it. --- Correct?

If I abandon the canonical viewing conditions the above considerations are no anymore true. (My objective can be different: instead of ultimate sharpness within a zone I may want to be able only to resolve a certain size i.e. perceive some adjacent things as different; I can found that the appropriate CoC implies so narrow DoF that I have to reconsider my sharpness requirements. Finally I may wish intentionally blur something.) That's why I added the words "required by the chosen criterion" in the DoF definition at the start of this message.

Sorry for so long message.

 

Andrey,

My answer to both of the questions you asked above is "Yes", but neither of those two scenarios address the issue being debated in this thread. Please respond to this:

When the subject space does NOT lie entirely at Infinity, but DOES include Infinity (1m to Infinity, for example, or even 100m to Infinity), focusing at the hyperfocal distance will allow us to achieve the desired sharpness with the widest possible aperture. Do you agree? (Previously, you said you "beg to differ", but the comments you've made more recently prove that you understand the principles involved.)

For THIS scenario, focusing at Infinity will require us to use a smaller aperture to achieve the same size CoC's at the nearest subject as we would at Infinity. Correct?

If you can answer "Yes" to both of these questions, then you must agree that Merklinger's method compromises image quality for the sake of convenience - it's just a quick and DIRTY way to select an aperture that will render near subjects sharply without having to worry about where to focus (we can just focus at Infinity.) It's "dirty" because stopping down further than one would if focused at the hyperfocal distance invites three forms of image degradation (discussed earlier).

Regarding our ability to accurately predict final enlargement factor and viewing distance: Completely ignoring considerations of final print size and viewing distance at the time of exposure will consistently produce poorer results than making SOME attempt to predict the final conditions. The only way to willfully ignore these issues at the time of exposure and actually come home with consistent results is to cover every possibility: You'd have to assume that every print will be viewed very closely, at a viewing distance of 10 inches (most adults with healthy vision can focus no more closely than this) -AND- you must assume it will suffer whatever enlargment factor can be delivered by the resolution of the lens and film together as a system. For the best lenses with color films, I consider this to be no more than about 9x, for the best black and films about 12x.

So, anyone who insists on ignoring decisions about print size and viewing distance at the time of exposure, should shoot EVERY scene with an aperture selected for a DoF that will deliver CoC's small enough to suffer 9x enlargement (or 12x for B&W) and a 10-inch viewing distance. That's excessive! Even our shortest lenses would have horrible DoF - requiring us to stay much farther away from the nearest subjects than we could were we to just make a decision about enlargement factor and viewing distance at the time of exposure.
Establishing a "cut-off filter" as you call it, by contemplating enlargement factor and viewing distance at the time of exposure, allows us to NEVER stop down more than we have to - and this translates to improved image clarity three ways. (Again: Wider aperture = less diffraction, less vulnerability to camera and subject motion, and perhaps an aperture that's closer to your lens' aperture of best resolution - usually near the middle of the aperture range.)

We CAN take control of ALL the variables that affect apparent sharpness instead of leaving them to chance or routinely stopping down more than necessary at the expense of diffraction, vulnerability had with longer exposures, etc. It only takes me three minutes to calculate this stuff in the field, for every exposure, using an HP48G+ (as described in the Word doc that can be found on the Tools page of my web site.) The results have been so spectacular, I can't imagine going back to guessing where to set the aperture.

Thank you,

Mike Davis

http://www.accessz.com

 

i must admit i could hear my brain crying pain as i try to understand the technical aspects of this focusing method.

 

Dexter,

I'm dying to know which method you're referring to -

Merklinger's focus-at-infinity method?

Conventional methods using hyperfocal distance?

Or conventional methods enhanced with considerations of enlargement factor and viewing distance?

Thanks,

Mike Davis

http://www.accessz.com

 

Mike,
If one accepts your criterion and all your prerequisites then there is no choice anymore, thus my answers are "Yes" to both your questions.

Let me explicitly state your premises:

1) The goal is to find optimal way (with largest possible aperture) to achieve a minimum acceptable sharpness from a range of distances of the scene.

2) Definition of the minimum acceptable sharpness: a point from the scene is said to be reproduced with minimum acceptable sharpness if the circle of confusion that the point produces on print is equal to linear resolution of viewer's sight.

3) The enlargement factor and viewing distance are predefined and are known at the moment of shoting.

4) Some other obvious and undebatable assumptions like that the lenses, film and paper are perfect (the diffraction may or may not be taken into account) etc.

The rest is the matter of technique. No one -- neither Harold Merklinger not John Smith -- can claim that he accepts all this premises AND has found any formulae that achieve the goal (1) better than well known traditional formulae; doing so would imply that mathematics is an inexact science. Your position therefore is invulnerable.

People say devil is in details. I'd better say the devil is in failure to find and critically analyze any silently made assumptions. If one want to attack your position he has to attack not a result, but the premises the result is based on.

For example I find the condition #3 not always acceptable; I understand and respect your argumentation but there are situations where I don't want obey this rule (in certain situations I may want the LINEAR resolution in space of objects be kept constant; it depends on my objective, depends on whether the print will be on the wall and be viewed from a reasonable distance or will a portion of the negative be enlarged and I must be sure the shapes on this fragments are recognizable); inevitable consequences of such a whim is that traditional formulae may become not optimal anymore.

(An curious aside: there is another seemingly weak point for attack: the definition of sharpness. The statement (2) roughly speaking tells the following: the lens maps a point to a circle, but the size of this circle is the maximum size that can be resolved by viewer, therefore the viewer perceives this circle as a point. The net result is "point to point" and it probably means a sharpness. --- This reasoning could be 100% true if the viewer's eye had an ability to de-blur the circle back to a point. But it hasn't. Another observation: the above definition of sharpness is based on metamorphoses of the single point, but sharpness is rather an attribute of a shape, of a continuum of points; hence the following argument: the CoCs from neighbor points of the scene do partially overlap, the image of one point is partially mixed with image of another one and even in the best case the net result should be "point to point, minus some contrast". --- Actually this issue is worth a more thorough investigation. I tried to do some rough estimates, and good news is that the statement (2) seems to be a good criterion. My point is that this statement is not in the least obvious.)

To sum up: if I assume all your premises then indeed the Merklinger's method is a quick and dirty method to do the job.

It would be unfair if I didn't mention the assumptions the Merklinger's method is based on. The narration in his articles is clear enough but I suspect some misunderstanding still exists. So please tolerate me with my broken English some time more.

(continued in next message)

 

Andrey,

While we wait for the second half of your last post, I thought I'd reply to what you've stated thus far.

You wrote:

"Mike, If one accepts your criterion and all your prerequisites then there is no choice anymore, thus my answers are "Yes" to both your questions."

OK, that's fair. I'm glad you agree.

"Let me explicitly state your premises:

1) The goal is to find optimal way (with largest possible aperture) to achieve a minimum acceptable sharpness from a range of distances of the scene.

2) Definition of the minimum acceptable sharpness: a point from the scene is said to be reproduced with minimum acceptable sharpness if the circle of confusion that the point produces on print is equal to linear resolution of viewer's sight.

3) The enlargement factor and viewing distance are predefined and are known at the moment of shooting.

4) Some other obvious and undebatable assumptions like that the lenses, film and paper are perfect (the diffraction may or may not be taken into account) etc."

I can accept your interpretation of my premises.

"The rest is the matter of technique. No one -- neither Harold Merklinger not John Smith -- can claim that he accepts all this premises AND has found any formulae that achieve the goal (1) better than well known traditional formulae; doing so would imply that mathematics is an inexact science. Your position therefore is invulnerable."

Thank you.

Regarding your comments about premise #3: As I wrote higher up in this thread, if we don't make the choice prior to exposure and then adhere to that choice later, the only safe way to shoot is to assume that every image will suffer the greatest possible enlargement factor and that it will be viewed very closely (at a distance of 25 cm).

Again, if we refuse to consider enlargement factor and viewing distance at the time of exposure, this is the only safe alternative. Any "whim" that comes along BEFORE the exposure is made, should be addressed by adjusting the CoC diameter used for DoF calculations right then and there. And any "whim" that comes along AFTER you make the exposure had quite simply better be a "whim" to reduce enlargement factor below that which was anticipated or a "whim" to increase viewing distance. In ALL cases, the traditional formula is inescapable. There is no way to ignore it without compromising something.

"To sum up: if I assume all your premises then indeed the Merklinger's method is a quick and dirty method to do the job."

This reads as if there exists a circumstance, where one or more of my premises are not in effect, in which Merklinger's method is "clean".

Please answer this question: What is that circumstance where it is better to throw away all the DoF that resides beyond the plane of sharp focus by focusing at Infinity?

Please don't take us full circle back to discussing scenarios other than the one in question here - where some portion of the subject space falls short of Infinity.

You've come very close to admitting that Merklinger's method always compromises image quality for the sake of expedience, but you are still making tangential arguments that don't address the issue.

You wrote: "It would be unfair if I didn't mention the assumptions the Merklinger's method is based on. The narration in his articles is clear enough but I suspect some misunderstanding still exists."

This too is a weak rebuttal - suggesting that if only we understood Merklinger's method, we would see the value of it. I fully understand his method. It's a gimmick – a clever shortcut that compromises image quality. Here's a page written by the man himself. (Do read the whole of it at your leisure, but for right now, please consider only the photograph and its caption.):

http://home.fox.nstn.ca/~hmmerk/DOFR.html

Martin Tai stated he believes using the conventional method vs. Merklinger's method "is a matter of choice." He wrote, "when objects, scenes at distance are predominant then use Merklinger way, focus at infinity."

Please examine the photograph at Merklinger's page, above. Is that cannon and the ground on which it is setting "predominantly at a distance"? No it is not. Now read the caption under the picture. Read it again and again - those are Merklinger's own words. What is there to misunderstand Andrey? Merklinger is WRONG! The statement made in that caption is RIDICULOUS.

(Continued in next post...)

Mike Davis

http://www.accessz.com

 

(Continued from previous post...)

Can't you agree Andrey that were we to calculate DoF such that our maximum permissible CoC's were no smaller than those Merklinger has produced in the foreground of this image we could select an aperture that is WIDER than the one Merklinger used to shoot that picture (by focusing CLOSER than Infinity, precisely AT THE HYPERFOCAL DISTANCE, producing comparable results without WASTING the DoF that resides beyond the plane of sharp focus)?

Merklinger either finds the foreground CoC's to be acceptably small in that photo or he has sacrificed their sharpness to maximize that had at Infinity. Which is it? He writes in the text that follows the photo: "The foreground is admittedly not tack-sharp." Gee, sounds like a compromise to me! He goes on to write: "Had I focused at the hyperfocal distance the telephone poles in the village would have been almost erased, and windows in buildings would have been just blurs."

Andrey, don't you find it conspicuous that Merklinger again fails to qualify his use of the phrase "hyperfocal distance" with the CoC diameter specified for the DoF calculations? In fact, he has failed to qualify a LOT of important variables affecting perceived sharpness!

Even with 1/30mm CoC's at the near and far sharps, the ENTIRE image would appear "tack-sharp" if the combination of viewing distance and enlargement factor was not sufficiently demanding to allow the viewer to resolve those CoC's. Right?! Give me any combination of enlargement factor and viewing distance and I can come up with a
CoC diameter most people will be unable to resolve. DoF calculations made with this CoC diameter will produce images that ARE "tack-sharp" when focusing at the hyperfocal distance (ignoring other factors that limit the total system resolution.)

Speaking of ASSUMPTIONS: Please read the last two sentences of Merklinger's "Introduction" section. Merklinger says that if we focus at the hyperfocal distance, we "will have sealed in that 'minimum acceptable standard' ". What standard is he talking about? Higher up he explains that he's talking about a 1/30mm standard for maximum permissible circles of confusion at the near and far sharps.

Mr. Merklinger! Will you please tell me what's preventing us from ABANDONDING that standard? Will you please tell me why we can't calculate DoF tables that give us apertures and hyperfocal distances that produce SMALLER circles of confusion than this standard you find so disappointing?

Merklinger's entire argument for avoiding hyperfocal focusing is fallacious! Don't you see that he is ASSUMING we are stuck with 1/30mm CoC's? In my opinion, the man knows better. He's just scratching up an excuse with which to argue that his technique will yield better results when the truth is it doesn't work as well as doing things the old fashioned way.

Merklinger says we'll be "guaranteed" to have "mediocre" results if we focus at the hyperfocal distance. That's ONLY TRUE if we join him in pretending that 1/30mm is the ONLY diameter CoC we can use in our DoF calculations!

In the paragraph immediately below the picture on Merklinger's page, he writes: "The hyperfocal distance for a 90 mm lens at f/8 is 106 feet." Harold! That's the hyperfocal distance for a 90mm lens at f/8 with a maximum permissible CoC diameter of 1/30mm!!! It is not THE ONLY hyperfocal distance! It is one of MANY POSSIBLE hyperfocal distances that could result with various choices of CoC diameter.

If I CHOOSE to make my CoC's SMALLER than the 1/30mm "standard" that leaves you so "bothered" by "old story about maximizing DoF by focusing at the hyperfocal distance", I can achieve any degree of sharpness I desire, right up to the limits of total system resolution! And YOU can TOO!

It's simply amazing that a man who wrote an essay titled "The INs and OUTs of FOCUS" could pretend to miss the fact that we can CHOOSE any CoC diameter we want for our Near and Far sharps and thus produce perfectly acceptable images while focusing at the corresponding hyperfocal distance. There is NOTHING wrong with focusing at the hyperfocal distance. You simply have to calculate DoF with a CoC diameter that's aggressive enough to suit the anticipated enlargement factor and viewing distance.

When I challenged Martin Tai with: "Please explain what advantage focusing at Infinity offers over "the conventional DoF method" when "scenes at a distance are predominant." There is no advantage. "

He simply said: "Sure there is, great advantage" and then failed to explain that advantage except to throw us this bone: "That is what focusing at infinity offeres: a sliding coc, smaller coc for far object, larger coc for near objects." So what? I responded with a question he has yet to answer:

"Your preference for making the far CoC's smaller than the near CoC's means that you either permit the near CoC's to be resolvable (visibly out-of-focus) in the foreground so that you can use the same or wider apertures than you would if focused at the hyperfocal distance -OR- you don't tolerate soft foregrounds and do make the near CoC's unresolvable by stopping down to compensate for having focused beyond the hyperfocal distance. Which is it?"

Andrey, for the sake of all the people out there who may read this thread without the benefit of your ability to digest it as thoroughly as you have, can't you join me in putting this myth to death? How can you support Merklinger's contention that hyperfocal focusing will always produce mediocre results, when that contention is based on the assumption that hyperfocal distances are somehow permanently fixed to a 1/30mm standard for CoC's?

Mike Davis

http://www.accessz.com

 

Mike wrote"
"It's simply amazing that a man who wrote an essay titled "The INs and OUTs of FOCUS" could pretend to miss the fact that we can CHOOSE any CoC diameter we want for our Near and Far sharps and thus produce perfectly acceptable images while focusing at the corresponding hyperfocal distance. There is NOTHING wrong with focusing at the hyperfocal distance. You simply have to calculate DoF with a CoC diameter that's aggressive enough to suit the anticipated enlargement factor and viewing distance.
"<p>
I just don't like to use same coc for foreground/background.<p>

I prefer use larger coc for larger object and smaller coc for background object.<p>

 

Martin,

You wrote: "I just don't like to use same coc for foreground/background. I prefer use larger coc for larger object and smaller coc for background object."

You've taken us back to where we were a few days ago! You still haven't answered a question I asked then. Instead, you have only reiterated the statement which prompted me to ask the question in the first place! Your avoidance of this question may be seen by others as evidence that you are unable to defend your choice to use Merklinger's method:

"Your preference for making the far CoC's smaller than the near CoC's means that you either permit the near CoC's to be resolvable (visibly out-of-focus) in the foreground so that you can use the same or wider apertures than you would if focused at the hyperfocal distance -OR- you don't tolerate soft foregrounds and do make the near CoC's unresolvable by stopping down to compensate for having focused beyond the hyperfocal distance. Which is it?"

You have several times contended that Merklinger's method is a valid alternative that's a matter of personal choice, but you refuse to respond to my contention that his method compromises foreground sharpness -OR- it compromises shutter speed (by forcing the use of a smaller aperture than would be necessary if you just focused at a hyperfocal distance calculated to yield acceptable CoC's for the anticipated enlargement factor and viewing distance.)

Again I ask: Which compromise do you prefer?

No matter how you answer that question, we're left with this one: Why do you tolerate either compromise? Why are you "choosing" to shoot yourself in the foot? You said there was a "great advantage" to using Merklinger's method. Let us hear your explanation of this advantage!

Lastly: How long will you continue to be evasive? Surely you must realize that silence is as convicting as your refusal to directly address the arguments I've presented. Are you interested in communicating the truth, for the benefit of those less knowledgeable than you, or is your mission simply to save face? Do you want people to conclude that all your technical articles are suspect?

There are only two ways to preserve the integrity of your reputation as a resource for photographic knowledge: Agree with my arguments or give us a logical, defensible rebuttal to the challenges I've made.

Mike Davis

http://www.accessz.com

 

Gentlemen, I apologize for the delay, the cause wasn't a whim


TWO points are said to be RESOLVED if their images can be discerned, i.e. if we can recognize them as two different spots, not as a single blob. The magnification is not restricted.


Please note:


1) Resolvability is an objective property, it can be measured. Sharpness is a subjective impression.


2) Resolvability in this definition (a commonly used definition, by the way) does not imply sharpness; the images of two points can be arbitrary blurred, the two CoCs can be arbitrary large, only one thing is needed: the distance between them should be large enough. Very roughly speaking, the resolvability is more relaxed requirement than sharpness.


Harold Merklinger (further H.M., I hope he won't mind) speaks not about two points; he speaks about a disk in space of objects. The lens equation makes it equivalent to the definition above if we chose two ends of any diameter of the disk as those two points from the definition and if we say that two CoCs are resolved if they are tangent to each other (see the graph).


(Mike, please note: you used the term "resolution" in opposite sense. You spoke about resolvability of CoC by viewer’s eye: if CoC is resolved then it is visible, then the point is not sharp; resolvability=unsharpness (bad thing). And vice versa: if CoC isn't resolved the picture is sharp (good thing). H.M. (and I in all my posts above) have used the term resolvability in the sense of definition above: if an object of a given size is resolved then it is visible clearly enough (net necessary sharp but already cannot be confused with other objects); if the object is not resolved then it is too blurred to be perceived separately from other objects. To emphasize the fact that the object whose size we test is located in space of objects, H.M. suggested a special term "DISK of confusion"; it is by definition the minimum size in space of objects that can be resolved (or maximum size that cannot be resolved, -- it is the same), it is the threshold for linear resolution in space of objects. An example what resolved and unresolved objects look like can be seen at http://www.photo.net/photodb/folder?folder_id=75190 except very first photo. Yellow and orange blobs are leaves in foreground that were either smaller than DoC (unresolved, transparent even in the center) or greater (resolved, opaque in the center) but still not sharp. Please don't take it as self-promotion.


I still assert that the most technically correct way to describe the difference between the traditional and the HM's approaches is to say that the latter requires equal LINEAR resolution in space of objects at near and far DoF ends, and the former requires equal ANGULAR resolution. (If you're not sure please let me know, I'll post the proof, it is short). In particular, the threshold of angular resolution of traditional method is always = c/f (where c is acceptable CoC, f=focal length; and therefore the linear resolution in space of objects according _traditional_ approach is =s*c/f, where s is the distance to near or to far DoF end). Since resolution of human eye by its nature is an angular one, the traditional approach wins in most "normal" situations, but these are not all the possible situations.

 

"This reads as if there exists a circumstance, where one or more of my premises are not in effect, in which Merklinger's method is "clean".
Please answer this question: What is that circumstance where it is better to throw away all the DoF that resides beyond the plane of sharp focus by focusing at Infinity?"


It follows from my boring prelude above that the H.M.'s method is clear in situation when we have a strange requirement: linear resolution in space of objects must remains constant everywhere inside a given range of distances. How can one arrive at such a perverse objective? --- Consider the example: I'm standing on a balcony, there is a huge crowd below me, from my feet till 200, 300m... I’m a detective. I want to photograph all the people and my objective is: I must recognize on the photograph every face from 1m to 300m. In darkroom I won't mind to use any needed enlargement. I take the size of Disk of confusion ca 3mm, focus at infinity and push the button. --- I readily agree Mike, that you can calculate such a CoC that every face in this zone will be sharp when viewed from certain viewing distance. But I don't need any face to be razor sharp, IT IS NOT MY OBJECTIVE, not my mission! I want them to be recognizable only! And by the way, I suspect that making every face "sharp" requires narrower aperture that I needed for my dirty purpose ("sharp" means sharp for any enlargement I may want to use to recognize a face 300m away from me). --- I hope Mike you see what I call the "criterion" and why accepting this or that criterion can change the method. The example is rather unusual; this sort of mission is more suitable for technical (crime?) photography rather that for general landscape photography, but such situations are possible and legal.


Personally I see 3 virtues of H.M.'s method:


1) A convenient tool in unsharpness/sharpness control. Maximization of sharpness in a zone is only a part of this general task, even though a very important part.


2) Appropriate and natural tool when the mission is specified in terms of linear resolvability in space of objects.


3) The method does not depends on format, lens focal length, all I need to know is the diameter of aperture hole (and distances to subjects and their size, of course, at least approximately). This issue is rather an academic one, but it makes academic life easier.


I don't agree to consider this discussion as a process "Mike Davis vs. Harold Merklinger". I consider the two methods as two different tools that are intended for different tasks. Apples are as good as oranges.


About my notorious "beg to differ". I misunderstood your questions. You wrote: "So, please tell me how it's advantageous to focus at infinity and then stop down enough to achieve acceptably small circles of confusion at the near sharp, when those same DIAMETERS could have been enjoyed at a wider aperture (at both the near sharp and at infinity) were you focused at the hyperfocal distance." -- The word "diameters" I interpreted as DISKS of Confusion. Surely, the DISKS do grow unrestricted when focus is everywhere except infinity, hence the objection. --- It was my error, I sincerely apologize.

 

Mike wrote:
"It's simply amazing that a man who wrote an essay titled "The INs and OUTs of FOCUS" could pretend to miss the fact that we can CHOOSE any CoC diameter we want for our Near and Far sharps and thus produce perfectly acceptable images while focusing at the corresponding hyperfocal distance."<p>
That is absolute lie !
<p>Merklinger specifically discussed about selecting smaller coc, in fact 1/150mm coc in his book<p>


"There is NOTHING wrong with focusing at the hyperfocal distance. You simply have to calculate DoF with a CoC diameter that's aggressive enough to suit the anticipated enlargement factor and viewing..."<p>

Ah, so convienient !?
For my requirement, I need a coc of 0.01mm instead of 0.033mm.<p>
According to St. Mike, I "have to" and "simply" "calculate" DOF<p>
Ok suppose I followed St. Mike's advice, and start to calculate
I usually use f8 on my Carl Zeiss Planer 50/1.4. <p> Opps, I don;t
have a calculator with me <p> Go home and find a calculator<p>
Yep, I got the hyperocal for f8, it reads 31.1 meter<p>
Unfortunatly, the dumb Carl Zeiss engineer did not anticipate
that some one like St Mike wanted 31.1 M marking on the dial.<p>
On my Planer, from 10 M to infinity, there is no marking in between<p>
St. Mike, sir, how do you put 31.1 M ?<p>
The next day, I happen to use my Carl Zeiss 35-135 zoom, I want to use a setting of 120mm @ f11. Oh, my god, according to St. Mike
I again "have to" "simply" calculate another hyperfocal distance...I diligently followed St Mike's instruction and plug the number in
my calculator, (which from now on, I must carry with me, to calculate
the hyperfocal distance of my zoom lens, which has infinite choice
of focal length) and lo, it is 131 meter<p>
I tried straining my eye to figure out where to put the 131 M hyperfocal distance on my lens ..."<p>

Next, I use the zoom at about focal length = 95 m, f8<p>

I "have to" "simply" calculate another DOF again ???<p>

<P> Forget it. If I follow St. Mike, I "have to" spent a lot of
time plugging on my calculator instead of taking pictures.<p>

<p> What the heck ! It is by far simpler to follow Merklinger put the lens at infinity and shoot.<p>
<p> It turns out St. Mike's that You "simply" and " have to" calculate DoF
is the most stupid method<p>

 

I did not answer Mike's "challange" because I am busy writing up on Scheimplug, Hinge Rules and View Camera DOF, which is inspired by another Merklinger's great work "Focusing the View Camera"

 

I tend to use small CoC for main object in the frame, with a wider angle lens this becomes less evident, but as said by Appleby, newer asph designs makes OOF-INF diference greater, I understand is the way Leica usage develops.

Then lots of philosophy about reasons for in and out of focus decition in a frame, with all my respect to Mr Adams, but is easy to decide every thing must be IN focus when contemplating one of his landscapes, but other tipes of photography requires other decitions, and other limits too.

Those who try to take all the advantage of the 5 and 10 lpm in a image, can be less worried about CoC in the OOF areas.

But that doesn´t make Martin post less interesting, thank´s for share, but I admit I just couldn´t read all.

 

Andrey,

I really appreciate your very lucid example of how a detective might willfully choose to employ Merklinger's method to select an aperture that provides just enough "sharpness" for the task at hand. You explained it very well and it truly makes clear the difference between the traditional method and Merklinger's method.

Merklinger himself does not make the distinction you have made - that his method satisfies a "perverse objective"... "rather than for general landscape photography." Indeed, he condemns hyperfocal focusing - see the link I quoted above, where he provides an example landscape photo. And unfortunately, his disciples don't have your depth of understanding about the limitations of his method.

Apparently due to lack of time, Martin Tai has still not responded to my questions about how image quality is compromised by Merklinger's method (something which you, at least, have acknowledged via your example). But: Martin has found the time to tell us it's difficult to implement the traditional method.

I suppose we'll have to conclude that Martin does indeed prefer to compromise image quality for the sake of convenience. That is certainly his perogative and I defend his right to make that choice, but he seems terribly reluctant to admit that his choice compromises image quality or come up with a defensible rebuttal to that position.

I don't have to be a saint to make the choice to use a calculator in the field for each and every shot. This ensures a quality that can not be achieved using Merklinger's method. I deal with the issue of where to focus by using a laser rangefinder. Having measured the Near and Far sharp distances, I calculate both the working aperture and the distance at which I should place the PSF. Then I use the rangefinder again to find a target that is precisely at the calculated PSF distance. I swing my camera onto that target, even if it is outside the intended image space, focus on the target, then re-establish the desired composition to make the exposure.

Yes, this technique is inconvenient, but I find it odd that Martin would object to the effort required for such procedures given that he is a large format photographer willing to go to great lengths to determine tilt angle, for example. His comments continue to appear evasive rather than constructive.

Unfortnuately, we've offended each other getting to this point. My goal has only been to set straight this thread for the edification of future readers who might jump on the Merklinger bandwagon in ignorance. At this writing, I think anyone who reads the entire thread can conclude that the convenience of Merklinger's method is had at a cost of image quality, that its application is best reserved for odd situations where you specifically want to limit "sharpness" to something less than that which can be resolved by the viewer in the final print at the anticipated viewing distance - a conscious decision to stifle image quality. Let's hope this thread will help prevent others from making an unconscious choice to degrade image quality.

Thank you,

Mike Davis

 

Mike, glad to have been of help. EVERY method has its own limitation, either explicit or implicit, and converting the latter to the former is not always a trivial task; here we had to exchange several posts before we've reconciled our positions.


Any further study that shows that we might have missed something important is welcome.


Thank you.

 

In landscape photography, the important object is at distance and
close up objects such as grasses, are not important. <p> Any method
has compromise<p>
<img src="http://www.photo.net/photodb/image-display?photo_id=857465&size=lg"> <p>The above Peggy's Cove pictures was taken with a
Minox 35ML at infinity setting<p> In the foreground, there is a
rope. Why should I chose to make the rope as sharp as possible and
make the fishing hut fuzzy ? I prefer the far zone very sharp
I just don't care the rope shows every strain of fibre<p>
It is a matter of choice.

 

Martin,

Your most recent post once again argues that infinity subjects can not be made acceptably sharp without focusing at infinity and you continue to ignore the questions I've asked above - questions which have you backed into a corner. You neither acknowledge nor offer evidence refuting the fact that Merklinger's method compromises image quality for the sake of convenience.

Without clearly stating that image clarity is compromised with Merklinger's method, you do the community a disservice by suggesting that Merklinger's method is merely a matter of personal choice. Again, I'm willing to defend your choice to degrade image quality for the sake of convenience - that's certainly your perogative - but I take offense to your unsupported insistence that the convenience can be had without impact to image quality, and much moreso to any suggestion that this convenience can be had while actually improving image quality (vs. that had with hyperfocal focusing).

Readers of this thread should beware your implication that hyperfocal focusing is somehow inferior to focusing at Infinity. Merklinger is wrong. You are wrong. I invite them to read this entire thread before drawing any conclusions.

Mike Davis

 

Martin, In all fairness to Mike, you have a track record in all your threads to ignore what has been written before you and never respond to questions that may doubt your position. This makes forum discussions very difficult for anyone to follow.

 

Mike, why dont' you show some of your picture showing why do you think
hyperfocal is better in landscape photography.Mik

 

Bill, I don't know what "track record" your are talking about. There is a very long discussion thread in LF forum, where I answered every question to the very end. You were the one who quit. Not me. That is your track record
http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=003Rdn
Mike also tried to mess up without even answering any question raised in that thread.

 

Mike, have you really read Merklinger's books and understand what
he wrote ?
Tell us, what he wrote in Chapter 9 of Ins and Out of Focus ?<p>

If you want to criticise Merklinger, at least you must read his
books.

 

Bill
In another related thread

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=003XDC

You were so convinced by Graeme, that the DOF limits are curved.
But where were you i hiding when Graeme conceded "checked" at
the very last post ?
<p>
That is your "track record".

 

Mike wrote:
"Without clearly stating that image clarity is compromised with Merklinger's method, you do the community a disservice by suggesting that Merklinger's method is merely a matter of personal choice"

Nonsense !
Merklinger's method GREATLY enhance image clarity in Landscape
photography. You absolutely don't understand what Merklinger is
writing about.

 

The proof of the pudding is in the eating<p>

In thread
http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0031ni <p>

Richard wrote<p>"

I recently read carefully through Merklingers series of articles
on DOF for non LF (i.e. no movements) cameras which are presumably
covered in his book 'The Ins and Outs of Focus'.
After struggling for a number of years with DOF and soft landscapes using
wide angles in 35mm I was enthralled. Being a theoretical physicist I soaked it up,
worked it all out myself and did a bunch of in camera tests.
The result being that I have fundamentally changed the way I think about and take
these kind (large DOF landscape) pictures"<p>

In



http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=002JzL <p>

Steve wrote"
. Infinity sharpness using hyperfocal settings is just not
as good as having an infinity focus. This is noticable on the
200mm, 300mm, 400mm etc. Even when moving the hyperfocal distance
closer to infinity, the sharpness
at infinity is still not as good as the infinity setting"

<p>

So Mike, you see, once people through their own experience, find out
infinity focusing provide better landscape picture clarity,
no amount of your shallow theory can change. People can decide
for themselve.<p>

<p>BTW, Merklinger's Ins and Outs of Focus is completely sold out.
Mike's drum beat from his corner probably helps

 

Most Natural Method

Any one watching thing of interest, whether it is near of far always focus their eyes at object of interest. When you look at a house across the street, say 50 meters away, your eyes focus at infinity, not on some "hyperfocal" distance.
Mike said, that is no good, you "compromise clarity". Thou shalt focus your eyes the hyperfocal way.

 

I have found this thread interesting even though I do not pretend to have understood all of its details. I must admit that I find the Merklinger method counter intuitive, but I am happy to have my assumptions challenged and will give it a try. I have been disatisfied with sharpness at infinity using my (by Mike' standard) sloppy hyperfocal method.

Mike has made some challenging and interesting objections (whether he has read all of Merklinger's book or not); though I do find the process of using a laser rangefinder to calculate the critical hyperfocal distance somewhat impractical for all but the most demanding of landscape photographers.( I imply no slur on such admirable high standards) On this point I also wish that Martin would try and address the specific objections that Mike raises without getting too emotionally defensive.

The burning questions seems to be 1) why is focussing at infinity going to give better resolution (in all practical circumstances) than Mike's critical hyperfocal method of including infinity well within an acceptable (but critical)range?
2) If there is no practical difference, then why is it not better to use the critical hyperfocal method and get better resolution further into the foreground?

From what I understand from Mike's objections to the Merklinger method it seems he has a point in claiming that Merklinger has taken rather a lax and uncritical method of hyperfocal focusing to attack; in other words a bit of a straw horse.

Martin, since Merklinger himself has not come along to defend himself, please try to respond specifically to Mike's objections. Your disciplined input would be highly valued.
Thanks,

 

Robert, nobody explained this topic more clear and convincing then
Dr. Merklinger himself <p>
He explained this in great detail, covering every angle in his
book The Ins and Outs of Focus.<p>
I suggesst you get hold a copy and read it. This book is sold out
but can be found in used book market.<p>

 

Thank you Bill and Robert!

It's so nice to have two people come along and join me in asking Martin to get back on track with the debate. Until then, his refusal to address my unanswered questions suggests he knows he is wrong, but it leaves me frustrated at his having left the ring before settling this intelligently.

Again, I encourage future readers to absorb this entire thread.

Mike Davis

 

Martin.... In the other long thread you refer to, everyone in the thread accused you of not responding to specific questions, not just me. In our private correspondence, you randomly would respond to questions making progress impossible. The same applies in this thread....that is the track record I refer to. I think you have had some very valuable input and are very gifted at math, but you seem to evade questions that either you are uncomfortable answering, which makes it appear you can not defend your position. I was not trying to attack you personaly, but rather share my observations. Possibly you should re read some of those posts where everyone kept asking you to answer specific questions, just like Mike above?

And yes, in the end, I beleive Graeme was incorrect about DOF lines in tilted lenses. But during the exchange, you made it appear that you were hiding and avoiding his questions... in the end, occassionaly you came through. And to advise you, I was not involved in the nitty gritty at the end of that thread. But anyway, why not take this as constructive criticism and move forward, it certainly was not intended as a personal attack on you. If you perceived it that way, I do apologize. You have made some excellent contributions to these forums and I hope you continue.

I am curious to an explanation as why Mike Davis is wrong above. Many of us are open minded, we just want to understand why Merklinger defied the focussing principles (DOF) that existed for 200 years in photography. Although I am a huge Merklinger fan on tilt, I too struggle with his concept about focussing at infinity, and yes I read the entire book, twice! So please try to educate us.... to me, Mike Davis's explanation of his method makes good practical sense.

 

Bill, in the LF thread, I answered a dozen times Graeme's question
again and again, again and again. He just did not get it. He finally
got it. Graeme has good virtue, his perseverance and willing to learn, that is why I was willing to spent time in answering his questions, because I know he will come through. <p>
As for Mike, forget it. He doesn't even bother read Merklinger's book
If he did, and work throught it. He might get his answer. But I doubt
he knows enough math to read Merklinger, other wise he would grab
the opportunity to join in the "curved DOf" choir and launched another
attack on Merklinger, he kept dead quiet. I knew his knowlegde on LF DOF is 0


<P> Merklinger's book is the BEST ANSWER to all questions. I am not
Merklinger's spokeperson. I don't even know him personally. If you
have question, read it again and again twice is not enough.
Otherwise, Bill, why would you belongs to "curved dof" choir ?

<p> The whole purpose of my thread is a provide a pointer to his
books. That is all. Other people has score to settle, that is not
my problem.
<p>

 

Martin.... Otherwise, Bill, why would you belongs to "curved dof" choir? I never felt strong either way on this subject, till I spent the time to work it out. And I am not afraid to admit I had an error in my initial judgement. I am human, I make mistakes, and I certainy am not afraid to admit to them.

you wrote.... The whole purpose of my thread is a provide a pointer to his books. That is all. IF that is the case, then you should state that you will not explain Merklingers position, everyone should read the book and draw their own conclusions. In a way, it kind of defeats the purpose of these forums. If you do not have the time or the inclination to do such, that is fair. But most of your threads lead us on, hence the follow up threads... and things get carried away. Since you understand Merklinger very well, if you ever feel the need to educate us less fortunate, I would really like to understand exactly why you feel Mike is wrong. Mike does have a very strong math background, and I think he too would be open to an acceptable argument. BTW, I don't think Merklinger really explained why focussing at infinity is superior over standard DOF. He shows how he did not get results that matched his DOF tables, but that is not sufficient data, as this could have been caused by a multitude of reasons. My gut feeling is, Merklinger threw the baby out with bath water on this one..... once his conventional results failed, he was determined to create a better method. I understand his method, but in certain scenes (as mentioned in several posts above) I just can't comprehend how focussing at infinity can gain more sharpness in the scene! But I can understand how it would create less sharpness.

If you ever feel compelled to answer this, be sure to cc me with your response. There is not enough people that understand Merklinger well enough to explain this, but many of us sure are interested in learning.

 

Martin,

On what do you base your assessment of my math abilities? And what would my knowledge of large format math have to do with the questions you've refused to answer in this thread? There's no need to lash out at me this way. What we need are answers to questions that you've avoided like the plague for several weeks now.

The following are NOT math questions. Can you respond to them intelligently, without being evasive?

***

(Quoting my original July 10 post)
Focusing at infinity when any portion of the subject space resides at some distance short of infinity is a waste of useful DoF.

****

(Quoting my July 13 post)
You haven't answered my original question. Here it is again:

If the largest circles of confusion seen in the foreground, forward of the plane of sharpest focus, are "acceptable" (i.e. "small enough") when focused at infinity, would circles of this size not be found equally acceptable if they occurred in the background as well, when focused at some point short of infinity?

Yes or No?

Your "choice" to use Merlinger's method when the scene is predominantly at a distance clearly indicates that some portion of your subject falls short of infinity and you are enjoying at least some near-side DoF if you find the nearest subjects acceptably sharp. If that's the case, why are you choosing to waste the acceptably small, equal-diameter circles of confusion that lie beyond the plane of sharpest focus?

****

(Quoting my July 16 post)
If we share the goal of making both the near and far CoC's too small to resolve in the final print at the anticipated viewing distance, focusing closer to infinity or at infinity (such that the far CoC will be smaller than the near CoC) will require a smaller aperture than could be used if we instead focused at the hyperfocal distance. Your
preference for making the far CoC's smaller than the near CoC's means that you either permit the near CoC's to be resolvable (visibly out-of-focus) in the foreground so that you can use the same or wider apertures than you would if focused at the hyperfocal distance -OR- you don't tolerate soft foregrounds and do make the near CoC's
unresolvable by stopping down to compensate for having focused beyond the hyperfocal distance. Which is it?

Are you allowing foreground subjects to be visibly out of focus so that you can shoot at wider apertures or are you stopping down more than you have to keep the nears visibly sharp despite having focused too long?

****

(Quoting my July 26 post)
You have several times contended that Merklinger's method is a valid alternative that's a matter of personal choice, but you refuse to respond to my contention that his method compromises foreground sharpness -OR- it compromises shutter speed (by forcing the use of a smaller aperture than would be necessary if you just focused at a
hyperfocal distance calculated to yield acceptable CoC's for the anticipated enlargement factor and viewing distance.)

Again I ask: Which compromise do you prefer?

No matter how you answer that question, we're left with this one: Why do you tolerate either compromise? Why are you "choosing" to shoot yourself in the foot? You said there was a "great advantage" to using Merklinger's method. Let us hear your explanation of this advantage!

****

You've also neglected to respond to Robert Clark's August 10 questions, despite having made several posts since then.

****

(Quoting Robert Clark)

The burning questions seems to be 1) why is focussing at infinity going to give better resolution (in all practical circumstances) than Mike's critical hyperfocal method of including infinity well within an acceptable (but critical)range? 2) If there is no practical difference, then why is it not better to use the critical hyperfocal method and get better resolution further into the foreground?

From what I understand from Mike's objections to the Merklinger method it seems he has a point in claiming that Merklinger has taken rather a lax and uncritical method of hyperfocal focusing to attack; in other words a bit of a straw horse.

Martin, since Merklinger himself has not come along to defend himself, please try to respond specifically to Mike's objections. Your disciplined input would be highly valued.

****

I can't speak for the rest of the world, but if you continue to avoid these questions, I for one will have to conclude that in your heart, you know I'm right, but just can't bring yourself to admit it.
Merklinger is just a man, Martin. He wrote some great stuff and some bad stuff. You can't believe everything you read just because it's been published and I don't have to quote Merklinger's writings to make the points I've made. The sense of what I've written is speaking volumes to several people.

You challenge me to read Merklinger's book, yet just as with the questions I directed at you, you've also not offered a reasonable defense to my July 26 post addressed to Andrey, where I exposed Merklinger's writings at the web site referenced here:

****

(Quoting my July 26 post)
I fully understand his method. It's a gimmick – a clever shortcut that compromises image quality. Here's a page written by the man himself. (Do read the whole of it at your leisure, but for right now, please consider only the photograph and its caption.):

http://home.fox.nstn.ca/~hmmerk/DOFR.html

Martin Tai stated he believes using the conventional method vs. Merklinger's method "is a matter of choice." He wrote, "when objects, scenes at distance are predominant then use Merklinger way, focus at infinity."

Please examine the photograph at Merklinger's page, above. Is that cannon and the ground on which it is setting "predominantly at a distance"? No it is not.

[Agreed Martin?]

Now read the caption under the picture. Read it again and again - those are Merklinger's own words. What is there to misunderstand Andrey? [Martin?] Merklinger is WRONG! The statement made in that caption is RIDICULOUS.

[snip]

Can't you agree Andrey [Martin?] that were we to calculate DoF such that our maximum permissible CoC's were no smaller than those Merklinger has produced in the foreground of this image we could select an aperture that is WIDER than the one Merklinger used to shoot that picture (by focusing CLOSER than Infinity, precisely AT THE HYPERFOCAL DISTANCE, producing comparable results without WASTING the DoF that resides beyond the plane of sharp focus)?

Merklinger either finds the foreground CoC's to be acceptably small in that photo or he has sacrificed their sharpness to maximize that had at Infinity. Which is it? He writes in the text that follows the photo: "The foreground is admittedly not tack-sharp." Gee, sounds like a compromise to me!

[What do you think Martin?]

He goes on to write: "Had I focused at the hyperfocal distance the telephone poles in the village would have been almost erased, and windows in buildings would have been just blurs."

Andrey [Martin?], don't you find it conspicuous that Merklinger again fails to qualify his use of the phrase "hyperfocal distance" with the CoC diameter specified for the DoF calculations? In fact, he has failed to qualify a LOT of important variables affecting perceived sharpness!

Even with 1/30mm CoC's at the near and far sharps, the ENTIRE image would appear "tack-sharp" if the combination of viewing distance and enlargement factor was not sufficiently demanding to allow the viewer to resolve those CoC's. Right?!

[Right Martin?]

Give me any combination of enlargement factor and viewing distance and I can come up with a CoC diameter most people will be unable to resolve. DoF calculations made with this CoC diameter will produce images that ARE "tack-sharp" when focusing at the hyperfocal distance (ignoring other factors that limit the total system resolution.)

Speaking of ASSUMPTIONS: Please read the last two sentences of Merklinger's "Introduction" section. Merklinger says that if we focus at the hyperfocal distance, we "will have sealed in that 'minimum acceptable standard' ". What standard is he talking about? Higher up he explains that he's talking about a 1/30mm standard for maximum permissible circles of confusion at the near and far sharps.

Mr. Merklinger! [Martin!] Will you please tell me what's preventing us from ABANDONDING that standard? Will you please tell me why we can't calculate DoF tables that give us apertures and hyperfocal distances that produce SMALLER circles of confusion than this standard you find so disappointing?

Merklinger's entire argument for avoiding hyperfocal focusing is fallacious! Don't you see that he is ASSUMING we are stuck with 1/30mm CoC's? In my opinion, the man knows better. He's just scratching up an excuse with which to argue that his technique will yield better results when the truth is it doesn't work as well as doing things the old fashioned way.

Merklinger says we'll be "guaranteed" to have "mediocre" results if we focus at the hyperfocal distance. That's ONLY TRUE if we join him in pretending that 1/30mm is the ONLY diameter CoC we can use in our DoF calculations!

[Am I wrong Martin? Can't you see that Merklinger's "guarantee" of "mediocre" results with hyperfocal focusing asks us to believe that we have no ability to choose a finer CoC standard? He woke up one morning with a clever idea that's very convenient to implement and this is how he's trying to pawn it off on people who are unwilling or incapable of discecting his premise!]

In the paragraph immediately below the picture on Merklinger's page, he writes: "The hyperfocal distance for a 90 mm lens at f/8 is 106 feet." Harold! [and Martin...] That's the hyperfocal distance for a 90mm lens at f/8 with a maximum permissible CoC diameter of 1/30mm!!! It is not THE ONLY hyperfocal distance! It is one of MANY POSSIBLE hyperfocal distances that could result with various choices of CoC diameter.

[Can you nod your head at least?]

If I CHOOSE to make my CoC's SMALLER than the 1/30mm "standard" that leaves you [Harold] so "bothered" by the "old story about maximizing DoF by focusing at the hyperfocal distance", I can achieve any degree of sharpness I desire, right up to the limits of total system resolution! And YOU can TOO!

[Where is my thinking flawed here, Martin? What can Merklinger's writing's possibly offer to refute this?]

****

The ball is in your court. Again...

Mike Davis

 

Mike,

You have being attacking Merkinger's for years.<p>
YOu haven't even read his books ? <p>
What can I say ????<p>

 

Mike wrote:
"
Merklinger's entire argument for avoiding hyperfocal focusing is fallacious! Don't you see that he is ASSUMING we are stuck with 1/30mm CoC's? "

"Don't you see that he is ASSUMING we are stuck with 1/30mm CoC's? "


"That's ONLY TRUE if we join him in pretending that 1/30mm is the ONLY diameter CoC we can use in our DoF calculations!

Am I wrong Martin? " <p>
Mike I am afraid, you are dead wrong<p>

You are bound to make a fool of your self, if you pose yourself
as a 'critic,' without even read the author's books.<p>

Merklinger made no such assumption.<p> YOU assume that Merkingliner made such asumption.<p>
See P 71 of his book <p>

OK !!

 

Martin,

I haven't been attacking Merklinger. I've been attacking the quick and dirty of focusing at Infintity and then stopping down further than you would have to if you instead focused at something short of Infinity.

No one can find even one statement I've made about Merklinger that didn't relate to this single issue and his position on the subject, written in his own words at http://home.fox.nstn.ca/~hmmerk/DOFR.html, is quite clear.

Again, you have avoided the crux of this debate. Surely I'm not the only person wondering why you haven't answered the questions I've summarized for you this morning.

You have Merklinger's books, but you've chosen not to quote him. Why?

Will you please choose even one of my challenges and tell us why Merklinger is right (on THIS issue)? Why don't you start with page 71? You've suggested that were I to read this page, I would find out that I have made an erroneous assumption. But you don't bother to bring it out here in the open. Why Martin?

I'll suspect there's nothing on page 71 or any other page that can erase the FACT (not an assumption) that at this page:

http://home.fox.nstn.ca/~hmmerk/DOFR.html

Merklinger himself wrote the following caption under his own example photograph: "This scene, the village of Placentia in Newfoundland, was taken with a 90 mm lens set at f/8 and focused at infinity. As explained in the text, to have focused at the hyperfocal distance would have seriously degraded the image of the village, while making negligible improvement to the foreground."

Now Martin, can you tell me what unreasonable assumption I've made? No one has to read page 71 of his book to see that Merklinger himself is ASSUMING that the hyperfocal distance is based on a 1/30mm CoC standard he find's objectionable.

Where on that web page does Merklinger say, "Of course, if we were to use a hyperfocal distance based on a smaller CoC diameter, we could obtain better results in the foreground, with a wider aperture, without any visible degradation of the Infinity subjects." ?

I've made a reasonable assumption Martin. Merklinger is trying to dupe the reader into believing his Infinity focusing technique is superior to hyperfocal focusing.

Martin, please tell us what is written on page 71 of his book that can erase his having written THIS on that web page: "What bothers me even more is the old story about maximizing depth-of-field by focusing at the hyperfocal distance. If you follow that advice you will be guaranteed that scenes in the distance will never be resolved any better than mediocre. You will have sealed in that "minimum acceptable standard".

It's quite clear to me that Merklinger is suggesing his method is superior to hyperfocal focusing, but his argument ASSUMES that maximum permissible CoC's are FIXED at 1/30mm. Now you may find something where he talks about adjusting CoC diameters, but can you find anything he has written that addresses doing so IN THE CONTEXT of comparing Infinity focusing to hyperfocal focusing?

As Robert Clark said, my questions make sense whether or not I've read Merklinger's books. Please stay on track Martin. Answer the questions.

Mike Davis

 

Martin, Mike has put in a lot of work tabulating some very specific and interesting questions that he has asked over and over again. They are all now in a single post. Yet you continue to refuse to answer these specific and pertinent objections to this particular theory of depth of field.

I assume as photographers we all want to learn more about the issue of depth of field, if there is more to learn. You have brought Merklinger's theory to our attention, but to me it is not whose theory it is that is important, it is what that theory is saying,what it adds potentially to our understanding. Certainly, given what we know of depth of field theory, what Merklinger says is counter intuitive - it goes against what we have learned and what seems to make good sense to us. Combine this with Mike's very cogent challenges, which are begging to be addressed and your refusal to come back to these specific points and it seems you are indeed avoiding rational debate.

The refrain: 'read the book, read the book' is simply not an acceptable response. It is like me trying to convince you of certain Christian Scriptural arguments and when you come back at me with reasonable objections to them I just tell you to read the Bible. You would be right to complain, asking why can't we examine the arguments about living or belief without having to take on a theological education.

It is the same with this issue: it is the comparitive merits of a 'Critical Hyperfocal Method' and the 'Infity method' relative to better and sharper picture making that is interesting. I do not want to become a Merklinger 'convert'. You made out the case for Merklinger quite forcefully at the beginning of this thread, attempting to explain the theory. When others have raised objections to the logic of the arguments they have been presented with you have been dismissive. Either you have dismissed people for their weakness at maths (surely the worst of unfounded assumptions, as well as insulting) or for their having not read your canonical text. This is tedious and frustrating.

You seem not to want to continue arguments that you started when the objections to those arguments become specific and dig into their unexamined assumptions. Your responses since Mike's arguments became very specific, pertinent and interesting seem to have grown weaker, more evasive and more antirational. You seem to be defending Merklinger as an article of faith and have abandoned the reasonable, careful debate that could lead to a deeper understanding useful to photographers of landscape.

 

Robert... you wrote in the above paragraph....
You seem not to want to continue arguments..........

My sentiments exactly, your prose was much better than mine. I tried to convey these same thoughts to Martin. Both you and Mike make perfectly valid and sensible arguments. I guess at this point, unless someone can validate Merklingers position, we must assume that this was just one mans approach to simplifying his photography, but in no way has it justified improving the on-film sharpness.

I also agree with Robert, that Merklinger is a human like us, he makes mistakes too. Martin, I read Merklingers book twice, and reading it a third time will not change my position. The justification I am looking for does not exist. But we have all remained open minded for you to educate us on what we are missing. If you, or someone else can not step up and help us novices out, then we must assume the old time tested mkethod of DOF still prevails.

As you can tell Martin, I am still not the only one who sees your style as frustrating in these threads. Once again, if you ever come up with a good argument against Mike, please cc me, I am very interested in learning the justification of Merklingers method.

 

Mike wrote:"You have Merklinger's books, but you've chosen not to quote him. Why?"

Because I want simply to emphasize the fact that a critic must read
author's main book. <p>
You don't criticise a movie, by not watching the movie, and base
on website. <p>
Website sell books, not to replace books. There are great amount of
information, detail arugments, examples, not shown in webpages.<p>

It is a simple fact, Mike has never read Merklinger's book, and refuse to do so<p>

Any one who are interested in serious discussion about Taosism
first of all must read LaoTzu. Any serious discussion of SunTzu
must based on SunTzu's writing, not secondary sources. Period<p>

 

I'm with Mike. I mean, I'm not boasting or anything, but 1/30 mm diameter coc is just not a reasonable assumption.

 

Rob, perhaps Merklinger has a problem here.

 

Still, you can't deny the visceral appeal of the sliding coc concept.

 

Dr. Merklinger is very smart scientist
He was elected Fellow of American Acoustic Society in 1981
DOF theory has being around for a long time. Every one knows how to use smaller coc then standard 1/30mm on 35mm camera. Any junior high school student can program their programable calculator to calculate any DOF with any coc they want to. No big deal there.
Classical DOF theory is based on circle of confusion on FILM PLANE ie, behind the lens.
Dr. Merklinger's major contribution to the theory of depth of field is his analysis from THE OTHER SIDE OF THE LENS, ie from the object INFRONT of the lens.
Following his analysis, he introduce a new concept, DISK OF CONFUSION. These two contributions, Object Field DOF and Concept of DISK of CONFUSION are enough to establish Dr. Merklinger as a great DOF author of last 100 years.
Dr. Merklinger packed a lot of information into his INs and OUTs of Focus Just list a few:

• Detail mathematic deduction of CLASSICAL dof formulas. Most book provide formular for near/ far limit, but never went into details of what are the condition for derivation, how are the formula derived. This alone, already enough to make this book a must have reference book on any serious photographer's shelf.
• Epoch making theory of Object Field DOF theory. He won by default, over 100 years, nobody looked at DOF from IN FRONT of the lens.
• Detail analysis of effect of defraction
• Convolution
• How to intentionally blur images, by choosing appropriate DISK OF CONFUSION.
• Discussion of Defraction
• Effect of Film plane curvature in shapness
• Very smart method for fans of small coc to find the hyperfocal distance of any small coc, say 1/150mm, 1/200 mm ....
• ......

• I find the INs and OUTs of Focus the best monograph on the topic of Depth of Field.

 

OK Martin,

I ask, and I ask, and I ask you to respond to hard-hitting, pertinent, technical questions that get right to the core of this debate, but you refuse to deal with them. I know you have the intelligence to handle them, so that's certainly not the problem. I'll spare you all the adjectives that come to mind.

Multiple people have told you as politely as they can that you are out of line, but you just keep coming back emptyhanded. Instead, you argue that my math skills are lacking, or that this is a purely subjective matter, or that I'm just out to get Merklinger, or that hyperfocal focusing takes so long it's "stupid" - anything and everything except facing the challenge I've presented so clearly.

Now you've sunk your teeth into another completely worthless argument - "Mike Davis is bashing Merklinger without reading his book. He hasn't read his book so how can he criticize him? What am I supposed to say?"

Merklinger's book is the evidence YOU brought to the table Martin, but you refuse to expound on it. Why? Is it because you're hoping upon hope that I'll never read it and discover there's nothing in it that can refute my contention? Maybe that way, this nightmare thread will come to an end and you'll be able to save face on a manufactured victory condition?

Sorry. Not today. Back to reality Martin. Fasten your seat belt. I've taken your challenge even though you ignore mine. The "INs and OUTs of Focus" is available for download at

http://www.trenholm.org/hmmerk/download.html

I've now read it in its entirety Martin. Guess what I found? All kinds of stuff to support my argument. You're just going to run to ground like you always do, making a lot of noise that has no substance, but I'll not be wasting my breath. Your goals are indecipherable, but my goal has been to bring to light the truth about focusing at Infintity. I just want people to understand the limitations that come with what it offers.

Merklinger's book contains the very same arguments that his web page showing the example photo has.

On the one hand, without question, you can find evidence that he really understands that there is useful DoF beyond the plane of focus -AND- that CoC diameters can be made small enough to produce sharp images while hyperfocusing. I never doubted his knowledge of this, but his book at least proves that he's aware that hyperfocusing really can produce sharp images. Best of all, his book proves that HE KNOWS his focus at Infinity technique produces compromised images. Stay with me...

Consider his Rule of Thumb #6:
"The zone of acceptable delineation of the subject falls equally in front of and behind the point of exact focus (not 1/3, 2/3!)."

Which prompts me to once again ask the question: Why would you want to throw away the "acceptable delineation of the subject" that's availble BEYOND the plane of focus when focusing at Infinity?!

Or his Rule of Thumb #20 (from page 71):
"The usual depth-of-field scale is calculated for a 1/30 mm circle-of-confusion. Typical 35 mm films and lenses are capable of delivering a 1/150 mm standard. To convert an existing depth-of-field scale to a new (higher, more demanding) standard, all we have to do is multiply the numbers on the depth-of-field scale by the improvement factor we desire. To go for that five-fold possible improvement, multiply all the numbers by 5: Instead of f/2, read f/10. Alternatively, divide the f-number you are actually using by 5 and look for that spot on the existing depth-of-field scale: if you are using f/11, look for the f/2.2 depth-of-field mark. And, if you wish, you can use different standards for the far limit of depth-of-field and for the near limit."

Martin.... if this is what you were referring to when you suggested I see page 71, answer this (in my dreams): How does this text disprove my conclusion that Merklinger's argument at his web site with the cannon photo is based on the assumption that we're stuck with a 1/30mm CoC standard? It doesn't. You were just scratching and clawing at the dirt. This rule from page 71 reveals that the man acknowledges that DoF tables can be tailored to be as aggressive as we need them to be.

But: You can also find statements like this:

From page 21:
"In general, I have found the results obtained using the time-honored methods usually yield backgrounds which are on the fuzzy side."

Here's where he begins to get silly, just like he does at the web page I referenced, in an effort to sell his method. My questions is (and has been): Is he pretending there's only one CoC diameter we can use for hyperfocusing? If not, there's no excuse for fuzzy backgrounds!

Rule of Thumb #4:
"If we want anything at infinity to be critically sharp, focus at Infinity."

That doesn't jive with Rule #6. Why would you focus at Infinity if "The zone of acceptable delineation of the subject falls equally in front of and behind the point of exact focus."?! As I've asked you many times Martin, if you find the DoF in the foreground to produce acceptably small CoC's (or disks of confusion, as Merklinger calls them), why wouldn't these same sized CoC's be acceptable beyond the plane of exact focus? Hello?

And his Rule of Thumb #23:
"A gentle repeat reminder: when you focus at the hyperfocal distance, you are guaranteeing that subjects in the distance will be resolved no better than your specified minimum standard. In order to improve upon this, you must focus beyond the hyperfocal distance."

Ahhh... here he suggests the possiblity that we can use a standard of our own choosing (a la Rule #20), but when he suggests that we focus beyond the hyperfocal distance to improve the sharpness of distant subjects, he NEGLECTS to mention a critical point: If our chosen standard were aggressive enough to begin with (smaller CoC's), we wouldn't feel moved to sacrifice foreground sharpness just to obtain acceptable background sharpness!

And in his Summary, Chapter 11:
"The traditional depth-of-field philosophy usually ends with the advice: to maximize depth-of-field, choose a moderately small lens opening, set the focus to the hyperfocal distance, and shoot. My parting advice would be a little different. For typical normal and wide-angle lenses, especially lenses having focal lengths less than about 50 mm no matter what the camera format, set the lens opening to somewhere in the 2 mm to 5 mm range, set the focus at infinity, and shoot. For lens openings larger than 5 mm, and for longer lenses that tends to mean all normal working f-stops, focus on what is critically important."

Focusing at infinity can not be done without forfeiting the DoF that resides beyond the plane of focus, thus the aperture you must chose to adequately resolve foreground subjects will be smaller than that which could be used if hyperfocusing instead! He chooses not to stop down that far and thus suffers UNSHARP foregrounds. Keep reading...

Under a photograph of a church with flowers very near in the foreground (page 60), he writes: "Taken with a 28 mm lens at f/11, infinity focus provided all the depth-of-field necessary."

Without question, if he's content with the CoC diameters in the foregound subjects, he could have hyperfocused and been just as content with his infinity subjects at something like f/8 (where the DoF that resides beyond the plane of focus could have been pressed into service instead of wasted!)

And on page 68: "Since working out these details, I find I do a lot of photography with the lens simply focused at infinity."

How convenient! But unlike Martin, at least Merklinger admits that the convenience comes at a price...

Don't miss these tidbits - an admission of compromise that's sorely lacking in all of Martin's defense of Merklinger's method:

From page 22:
"Objects photographed up close can still be recognized even if they are a little fuzzy. Objects in the distance may need to be very sharply imaged if they are to be recognized at all."

From page 48, under the infamous cannon and village picture:
"The cannon, the grass, the gravel, and the trees are clearly a bit fuzzy, but we have no difficulty in recognizing them."

From page 66:
"Experimenting, I learned that with the lens focused at infinity, things up close still seemed to be adequately sharp."

So Merklinger admits that his infinity focus foregrounds are "a bit fuzzy", "a little fuzzy" or "seemed to be adequately sharp."

I'm I making an ASSUMPTION Martin?

His method is clearly a compromise that is acceptable only if you are willing to suffer "fuzzy" foregrounds in favor of sharp Infinity subjects and a very convenient way to set focus and select aperture. The fact remains that everything in the shot can be made at least as sharp as his Nears at a wider aperture than he's using - by focusing more closely than at Infinity. And, despite his negative comments about hyperfocal focusing, his own Rules #6 and #20 reveal that he knows one can achieve acceptably sharp Nears AND Fars by hyperfocusing for a smaller CoC diameter.

His method boils down to this: If you're willing to take a hit in foreground sharpness and waste the DoF that lies beyond the plane of focus, you can put convenience ahead of quality by focusing at Infinity and selecting an aperture that's just small enough to make foreground subjects only "recognizable".

No thanks! I'm not that lazy.

Mike Davis

 

Mike, now you have read the book.

Do you still insist that

" Merklinger's entire argument for avoiding hyperfocal focusing is fallacious! Don't you see that he is ASSUMING we are stuck with 1/30mm CoC's? " "Don't you see that he is ASSUMING we are stuck with 1/30mm CoC's? " "That's ONLY TRUE if we join him in pretending that 1/30mm is the ONLY diameter CoC we can use in our DoF calculations! Am I wrong Martin? " <p>


ARE YOU WRONG ? Mike ??

 

Mike, it is not nice, if you want to sell your method by attackimg
Merklinger<p>

<p> Why don't you introduce your<p>
small coc + Programable Calculator + Laser Rangefinder and find a stone method ?

<p> Don't be shy, it is time to hawk YOUR brand of goods

 

Thank you Mike for persevering and getting to the bottom of this. Your demystification of a theory, which turns out to be at best a useful focusing method for certain limited situations has been worth reading.

 

Thank you Robert. People like you have made it all worthwhile.

Mike

 

Martin,

You've been pressing the "Contribute an Answer" button for quite some time without contributing anything of value (in my opinion.) It's my turn to leave the ring. I have nothing more to contribute unless you get on track with the real debate.

Bye,

Mike Davis

 

Well said Robert, you took the words right out of my mouth! I think Mikes last paragraph sums it all up.... it's convenience vs. accuracy, a simple trade off. Like so many things in photography, there is shortcuts to simplify, often at the expense of accuracy. Until someone can dispute Mikes line items, I think this thread has ran its course. And BTW Martin, Mike is not pushing his "Brand" of DOF, he is reiterating the same DOF method / formula that has been around for 200 years! I wonder if this book went out of print, for some of the reasons stated by Mike?

 

Thanks Bill,

Mike

 

Mike left the ring, too shy to show his laser rangefinder DOF technique.
Have a look : Mike Davis Laser rangefinder DOF technique
Required equipment for Mike DOf TECHnique

• HP 48G Programmable calculator
• Optic Logic Laser Rangefinder, $279

• Use laser rangefinder to measure distance
  Spent 2 minutes in the field to do the calculation
  ...... Oh dear !

 

For Bill and Robert, fan of Mike Davis Laser Rangefinder DOF technique, I highly recommend the Leica Rangemaster as a must have equipment. It is more expensive than the $279 Optic Logic laser rangefinder, but Rangemaster has better quality.
Don't forget your lap top too.

 

Wow ! Mike Davis's Laser Rangefinder + broomstick DOF technique
makes very interesting reading. It is a good example of classical
DOF pushed to extreme <p>

"I use a Hewlett Packard HP 48G+ programmable calculator
to do this math in the field in less than 2 minutes. "<p>

I thought 2 minutes is all it takes, that is not too bad, but
wait a minute !! <p>

I use an Opti-Logic. 400XL Laser Rangefinder (available from CSP Outdoors
at: http://www.cspoutdoors.com, for $279.00) to measure the Near and Far
distances. The Nears are sometimes too close for the rangefinder to
measure (<12 feet) and I must switch to using either a 10-ft. tape measure
or a Digitape Sonic Tape Measure that is extremely accurate out to about
30 feet -"<p>

Oops, sorry, Mike, I made mistake again, ( I am human you know )I thought you need only a laser rangefinder,
aha, you need another pieice of equipment: a 10 feet tape measure.

Let see, you take the tape out, lay it on ground, and measure, how
much time it takes ? Another 2 minutes , so we spent 4 minutes
already<p>
"I indexed these labels in feet by advancing and focusing on a
broomstick that I propped at carefully measured distances from the lens," <p>

Oh, Mike, I see, for practicing Mike Davis Laser Rangefinder DOF technque, your followers need yet another piece of accesory : a BROOMSTICK !!


<p>

"Once I calculate the best focus distance, using the formulae above, I find
a target that is at that distance from the camera position using the laser rangefinder
-
the camera onto that object which I have found to be at the calculated
distance, focus on the target, then swing my camera back to reframe the shot with the intended composition."
<p>
I see, when there is really nothing important in that calculated
distance, Mike insists that his followers must find a piece of stone
rock or something to focus on, if there is no rock, stone, then
walk over and set up a broomstick.... How long it takes ?? If his
calculated hyperfocal distance = 30 meter, walk over there, set up
broomstick, walk back focus camera, walk over and remove the broomstick, at least back and forth three times, 3 x 30 meter,
his followers need to walk 90 meter to implement the broomstick
technique.. 20 minutes of walk. Good excercise in the field, good for
health !

Instead of pushing only one button-- shutter release, his followers
must push innumerous times on HP calculator buttons.... let finger
do the photography.

<p> How exortic ! What precision !!

<p>

<p>I think Mike Davis Laser Rangefinder with Broomstick technique
worth a place in the Guinness world record as the oddest DOF technique.

 

Great sliding cocs, Batperson! This has been an amazing thread! Since the free intercourse for which this web site was conceived has failed to come to fruition, one is forced to conclude that the main protaganists have no alternative, now, but to "agree to differ", as the cliché goes. (Cliché = trite phrase or saying, used by those incapable of original thought). ;-)

 

Martin, if you want to attack someone, at least recall their facts accurately. I read the Mike Davis link you referred to, he uses the broom sticks to create accurate footage scales for his lenses. You obviously must use a grond glass in the film plane to accomplish this. This is very clever time saver. You do your set up work once, then you know your cameras focus system is very reliable. When you want to focus at 50 ft, you can feel confident that setting the lens to 50ft will acheive that exact focus distance. This is something I should integreate into my own photography, as we all know that rangefinder cameras are not quite as accurate on focus distance as SLR cameras. So don't try to make this broomstick method act like some type of magic carpet...it is a clever trick, which I am glad you pointed it out, soon, I will introduce to my lenses also. It will speed up my field DOF methods.

Next, I have been using a laser rangefinder for over 5 years now. I find my near and far distances in the scene, I glance at my DOF cheat sheet (which has my preset cc's), it advises me what distance to focus at. Up till now, I used to find something at that distance, and focus on it, DONE! But with Mikes clever trick, I won't even have to do this anymore, I can just set the lens to the proper markings. I do this entire process in 15 - 30 seconds and I am assured to have the entire scene within my acceptable cc's. A programmable calc. is not required for this, but it can be used if you want to change variable such as cc. But for me, small cheat sheets is all I need... (but I do carry a TI - 89 for those special scenes)

As for your reccomendation of the Lieca rangefinder, I strongly do not suggest anyone buy this rangefinder. It measures from 11 yards, or 33ft, whereas the DMI measures down to 12ft. It is much more valuable to have the shorter distances vs. the longer. DOF is effected more by the close subjects than the far subjects. The DMI rangefinders are one of the few that read out in feet, which I am more comfortable in and they are very accurate.

Martin, I am really baffled by your approach to this thread. It seems now you have taken the position, if you can't beat the message, you start beating-up the messenger? That is not the purpose of these forums Martin. I still am hoping you spend as much time responding to the issues, vs. attacking the messenger. I know you are very bright, and I still look forward to your position on Mikes line items about Merklingers approach. If you do not want to respond, then let the thread die...

 

Well said Bill. Martin I am glad you have a sense of humour, but it is a pity that you cannot, with dignity acknowledge Mike's expertise and thoroughness. Not all of us want to be so exact and careful but that is a reflection of our laxity or casualness and no reason to deride others whose standards are higher.

Obviously if we want smaller cocs we should follow Mike's rangefinder method.

 

Bill, the problem with Mike's method<p>

1) Impractical with 35mm camera. Bill, tell you how do you focus
a Leica M or R at 30M ?<p>
2) More fundamentally, the question boils down to where do you
want your sharpest place to be ? As shown in the diagram, there is
only ONE sharpest razor edge. <p>
3) When main object of interest is at infinty, the only way to
allocate the sharpest point on that object is to focus at infinty
not a stone or nothing in between, and allocate the sharpest power
to in completely unimportant stone or nothing.<p>
4) After all his labour, his smaller coc is still > 0.02mm 50 lpmm. not good at all.
5) Leica lens is much sharper then 50 lpmm. Summilux 50 can resolve
up to 95 lpmm on developed film. You need at least 0.005 mm coc
to achieve sharpest far zone object. That can only be achieved by
focus at infinity.
6) Minox COMPLAN has even higher resolution, it resolves over 170 lpmm
on developed film. I need to get 350 lpmm that is 0.0029 mm coc
at that object. That can be easily achieved with Minox camera focus at infinity.Bill, can you show me how, with your Mike's method
achieve such size coc ? Give us an example.

 

Where to put the sharpest edge of lens ? <p>

No matter what small coc you chose, the sharpest point of lens
for object at infinity is always at infinity, don't waste the sharpest
lens on a piece of stone or gravel on something inbetween.

 

As example to show how focus at infinity brings out the best of lens's power. The following picture was taken with Minox B

 

Enlarge to 3.5 x 5"

 

Within the circled area, there is a street sign. Enlarge a small part of that sign 200x The " one " still can be resolved.
Such kind of highest resolution result for far object can only be achieved by focus at infinty.
Bill, show me a picture of yours, using Mike's method, enlarge a small segment 200x, will you ?

 

All Merklinger said was focus at infinity bring out the supreme power
of a lens, at its best on main object at infinity <p> With some sacrifice resolution a near zone ( As indicated by my table at
beginning of thread <p>

<p>In the above picture, the buildings at far zone is my main object
of interest. Those far zone object occupied the almost 95 % of all
the film area. Rendering those 95% area as sharp as possible
enhance greatly the overall sharpness of the picture, because 95% is
at sharpest coc, not 0.02, not 0.01, but around 0.004 mm. (estimate )

<p> At hyperfocal point there is some dirt, I don't want to render
dirt or stone as sharp as possible, and degrade 95% of my picture to
only 0.01 mm coc. Bill you may chose to do so, that is your artistic
decision.

<p> As for the often quoted Merkling canon picture, he stated, he
main theme of his picture was the small village build on a sand bar,
he want that village to be sharpest, at the maxium resolution of lens
permited, the canon is not that important. That was his choice.

 

When there are substantial object of interest in foreground, focus at infinity method can not be applied. Traditional DOF method is best suited for such situation
As described in my article about where to focus at at slanted field of tulips with SLR. Hyperfocusing a Field of Tulip Flowers

 

Martin, I agree that to photograph a subject at infinity the lens should be focused at infinity. It would make no sense, for example, to set the lens to a hyperfocal distance to photograph the moon.

However, photographs of landscapes often include middle- and foreground objects, as well as distant scenery, all of which should be acceptably sharp in the image if possible. To focus on infinity for such a shot is to reduce the zone of acceptable sharpness unnecessarily. So, in such cases, it makes much more sense to focus at a point closer than infinity (the hyperfocal length), so as to maintain acceptable sharpness for as much of the the foreground and middle-ground as possible, but not so close as to render the distant scenery visibly unsharp.

Exactly what the hyperfocal length should be depends, of course, on the lens's focal length, its aperture and the size of CoC that is required, be that .03mm or smaller. The smaller the required CoC, the more distant must be the point of focus in order still to have the distant scenery rendered acceptably sharp.

Of course, with a very small CoC the hyperfocal length would be so great that it couldn't be measured using the distance scale inscribed on the lens barrel and neither could the camera's rangefinder be used effectively. If that were the case, then I agree that there would be no point in trying to focus closer than infinity.

 

I challange Bill, Robert, Ray Moth to show me a 200x enlargement of
detail using Mike's method.

 

Martin, it seems you have become so defensive, that most or your arguments are no longer making sense. But to give you the benefit of doubt, I will respond to your issues, even though they have been addressed prior.

You wrote……Impractical with 35mm camera. Bill, tell you how do you focus a Leica M or R at 30M ?

I am sure this is a loaded question, and I do not use these cameras. But the point is, you focus at the distance required to meet your DOF requirments. If the camera does not have focus ranges, than use Mikes Broomstick method and mark the lens yourself. If your using a camera that can not be focussed than it should not apply to this discussion.

You wrote…. More fundamentally, the question boils down to where do you want your sharpest place to be ? As shown in the diagram, there is only ONE sharpest razor edge.

Yes, we all know Martin the point of exact focus will be the sharpest. So?

You wrote….When main object of interest is at infinty, the only way to allocate the sharpest point on that object is to focus at infinty not a stone or nothing in between,

Yes, you are stating the obvious. In Mikes method if there is nothing worthwhile in the scene, except infinity, then we all would focus at infinity. But that is not what this is about.
You wrote….

After all his labour, his smaller coc is still > 0.02mm 50 lpmm. not good at all. 5) Leica lens is much sharper then 50 lpmm. Summilux 50 can resolve up to 95 lpmm on developed film. You need at least 0.005 mm coc to achieve sharpest far zone object. That can only be achieved by focus at infinity.

This discussion has only resolved around DOF. Of course we all know there is a max. amount of resolution any film / lens combination can record. This is established by the formula, 1/R = 1/R1 + 1/R2 + 1/R3, etc.. Where R is the total resolution to film, and R1 through Rx represents the max. possible resolving power of all the cameras components such as lens, film, filters, etc. Velvia is the sharpest color film made today, and even with the sharpest lenses, approx. 55 lpmm is the highest resolvable lpmm to film. (and only at the point of exact focus) With Tech Pan, it is possible to get up to 95 lpmm to film. So one uses this as their max. on film resolution, assuming they want to achieve resolution this high. It’s the photographers option to pick the highest on film resolution or trade some of this resolution for increased DOF. It’s all about tradeoffs. However, what ever lpmm, or cc Mike chooses, this will be the lowest resolving portion of his image, and that is the goal, and the DOF formula will advise you exactly where to focus to achieve this. For some reason, I do not think you are grasping this point.

You wrote.. 6) Minox COMPLAN has even higher resolution, it resolves over 170 lpmm on developed film. I need to get 350 lpmm that is 0.0029 mm coc at that object. That can be easily achieved with Minox camera focus at infinity.Bill, can you show me how, with your Mike's method achieve such size coc ? Give us an example.

First off, I don’t know any film made today that can resolve 170 lpmm to film. I believe you are mistaken there. However, it is a mute point. Once again, enter your desired cc into the DOF formula, enter near and far, and you will get the focus distance required. And in the case of Minox, which was designed to photograph flat documents, well it’s a no brainer, focus on the document!

You wrote..No matter what small coc you chose, the sharpest point of lens for object at infinity is always at infinity, don't waste the sharpest lens on a piece of stone or gravel on something in between.

If that is the case, then Mike would focus at infinity also, it is only when he desires something in the foreground to meet a min. acceptable resolution will he enter the near distance in the formula, but if a scene is entirely at infinity, well, it’s a no brainer again! I can tell you are missing this portion of Mikes argument.

You wrote..Within the circled area, there is a street sign. Enlarge a small part of that sign 200x The " one " still can be resolved.

Not sure what you are tyring to prove here.. I can resolve a pole 400x too? I can still see it’s a straight structure, does that mean I resolved it to some standard? Or does it mean I can identify it is a vertical object. This discussion revolves around resolving to a known standard.

Such kind of highest resolution result for far object can only be achieved by focus at infinty.

Yes, no one will disagree with you. If your subject is at infinity, then focus at infinity, no argument, that will provide you with the PSF at infinity, the sharpest part of the scene. But what if you have something equally important closer than infinity, that is the point Mike was making! Do you get this Martin, I keep repeating it, and so does everyone else in this thread
?
You wrote..Bill, show me a picture of yours, using Mike's method, enlarge a small segment 200x, will you ?

It makes no sense what you are demonstrating. Your defensiness has taken your arguments to a new level.

All Merklinger said was focus at infinity bring out the supreme power of a lens, at its best on main object at infinity With some sacrifice resolution a near zone ( As indicated by my table at beginning of thread

Why are we still arguing this.. the sacrifice is exactly what Mike discussed. His point was, let the photographer pick the importance of each subject and how much is willing to be sacrificed.

You wrote..In the above picture, the buildings at far zone is my main object of interest. Those far zone object occupied the almost 95 % of all the film area. Rendering those 95% area as sharp as possible enhance greatly the overall sharpness of the picture, because 95% is at sharpest coc, not 0.02, not 0.01, but around 0.004 mm. (estimate )

I am willing to bet Mike, and others following this thread would all agree, under that circumstance, we would all focus at infinity. But it was our decision that 95% of the scene is most important, so we focus at infinity. Very simple!

You wrote..At hyperfocal point there is some dirt, I don't want to render dirt or stone as sharp as possible, and degrade 95% of my picture to only 0.01 mm coc. Bill you may chose to do so, that is your artistic decision.

Yes, this is very correct, and this is what we have been trying to convince you of, let the photographer decide, not Merklinger.

You wrote..As for the often quoted Merkling canon picture, he stated, he main theme of his picture was the small village build on a sand bar, he want that village to be sharpest, at the maxium resolution of lens permited, the canon is not that important. That was his choice.

Wonderful, and using the standard DOF he can make that his choice also and enter such in the formula and it will advise him to focus at infinity.

When there are substantial object of interest in foreground, focus at infinity method can not be applied. Traditional DOF method is best suited for such situation

So now you confess that focussing at infinity is not always best, even if infinity is part of the scene? If so, this thread was a waste. We all know if the scene is at infinity, focus at infinity, the discussion was about if there was subjects not at infinty that were equally important.

I challange Bill, Robert, Ray Moth to show me a 200x enlargement of detail using Mike's method.

If we all focus at the same point, use the same camera, lens and film, we should all get the same result, right? If you challenge Mike to get infinity at 200x then he can just as easily challenge you to get something less than infinity at 200x. But you are getting way to carried away, nothing is getting resolved at 200x anyway. But if you selected a more reasonable number, my argument still stands, i.e. wherever the point of exact focus is, we both will get the same on film resolution! Does this make sense to you?

Ray, thank you for clarifying these points to Martin. I think this thread is getting a bit rediculous.

 

Bill

Did I stated very clearly it is a matter of personal choice in the message with Peggy's Cove picture:

"The above Peggy's Cove pictures was taken with a Minox 35ML at infinity setting

In the foreground, there is a rope. Why should I chose to make the rope as sharp as possible and make the fishing hut fuzzy ? I prefer the far zone very sharp I just don't care the rope shows every strain of fibre

It is a matter of choice"

 

Bill wrote: "First off, I don’t know any film made today that can resolve 170 lpmm to film. I believe you are mistaken there. "

<p> FYI. Agfa Copex Rapid 600 lpmm, Fuji Super HR 850 lpmm

 

The critically important Mike's premise is accepting an anticipated enlargement factor and viewing distance. It is his key point. If one does accept this premise he MUST admit that there is a REDUNDANT sharpness at plane of sharp focus, and finally he will inevitably admit that Mike's method gives the optimal result. If one does NOT accept this premise he'd better to describe WHY, i.e. to describe a situation when it is better to refuse the Mike's premise to get an optimal result (and what 'optimal' means in this case).


Any further debates without explicitly clarifying one's choice relating to this premise are absolutely meaningless.


And after the choice is made there is no more room for personal preferences.


Any theory can only benefit from finding its own intrinsic limits. Martin, I regret that you sink down to such level of arguing. In truth, a clever criticism is much more health-giving for a method than a fanatical defense. Sorry to say that.

 

"The critically important Mike's premise is accepting an anticipated enlargement factor and viewing distance. It is his key point."

<p> From the start, it is his weakest and flawed premise. <p>
Why restricted oneself to "anticipated enlargment " ? Why restrict
on self to certain "viewing distance" ?

<p> I may want my Leica negative enlarge to 4x6", or 8x10", or 20x 30" or mural. No restriction.
<p> How do you limit viewer to certain "viewing" distance ? You hang
a picture on a wall, people like to take a closer look. How can you
limit people's view. What about some one take out a magnifier
and examine the detail .....

<p> Different premise and restriction yield different result
<p> Merklinger's method is not based on the limitation of naked human eye, which has very low resolution capability.
but based on what is really resolved.

<p> Apparent "sharpness" to the eye is not the same thing as resolved
<p> One picture may look pretty sharp. But when it may not stand
scrutiny under high power loupe or microscope. Where passed for :"sharp" by the eyes may turn out to be unrecongizable.
<p> On the other hand, resolved does not necessarily mean sharp to
the eye. It is two difference criteria.
<p> Merklinger's focus at infinity method, packs the maxium information content in to negative. <p>
<p> Suppose there are one thousand sign posts with letters along
a road, two meter apart, from 1 meter to 2000 meter. <p> With Merklinger's focus at infinity, as long as I choose the aperture
opening smaller than the width of the letter on sign post, all
the sign post letter will be resolved, from 1 meter to 2000 meter.

<p> Merklinger method is the method of maxium information content.
The sign post at 1 meter will be fuzzy, but from information stand point, the letters will be recongized by human or OCR.
<P> Focus at hyperfocal distance will not provide maximum information
content. It over resolve 1 meter cannot resolve far region.

<p> Classical DOF is only a method of fooling the naked eyes.

 

Since that's all I use to look at pictures with Martin, I'm quite happy with that.

 

Ok, Martin, great! We've finally got a real progress! No mocking!

We could save a lot of efforts and not torment each other if we at the very start clearly stated that the real difference is here, in accepting or refusing this premise.

"How do you limit viewer to certain "viewing" distance ? You hang a picture on a wall, people like to take a closer look. How can you limit people's view. What about some one take out a magnifier and examine the detail ....."

Ok, I also wrote about. My point is IF we accept Mike's restriction then the Mike's method is optimal. IF we DO NOT accept it, it can be NOT optimal.

Mike's premise is in my opinion a very realistic restriction. And having agreed to obey this restriction he takes 100% control of the sharpness. I'd call it a 100% success.

Have we always to accept this premise? --- No. I already showed the example with a detective where Merklinger's method is 100% optimal and Mike's is not. All depends on HOW we intend to use the photo, will we come closer and closer, probably with loupe (again no mocking) or just view it from a reasonable distance. I also have a questionable habit of inspecting my prints with my nose close to the print surface, but I won't affirm it is a 'normal' behavior. I also appreciate the fun when the print reveals more and more details at infinity when I come closer and closer to the print (for sake of this fun I can also ignore the fact that near details reveal more and more unsharpness). --- But it is not an argument in the polemic above. I'm absolutely sure Mike will never claim that his method is able to provide me such a fun, --- it is against his premise!

One may or may not accept the restrictions imposed by naked human eye, indeed THIS is matter of personal choice (or matter of intended usage of the photo) but it should be explicitly stated, and such a statement puts a stop to the mess.

"Classical DOF is only a method of fooling the naked eyes."

Exactly! But many viewers are absolutely happy when their eyes are fooled in appropriate way. Mike doesn't promise anything more.

Well, happy end?

 

That's the best line in this entire thread! LOL!!



Mike

 

Classical DOF is only a method of fooling the naked eyes. I guess Robert and I are the only ones here without bionic eyes.

 

Martin, I give up on the DOF issue. Either you have set up a mental block in your head to not accept what we are explaining or you have too much pride to acknowledge some of what you (and Mr. Merklinger) beleived is a flawed. At least give us credit for trying. But we can only repeat the same thing so many times.

Martin wrote....
FYI. Agfa Copex Rapid 600 lpmm, Fuji Super HR 850 lpmm

I am shocked any film can resolve this high, but even so, after you run it through the 1/R formula for total camera system resolving capability, 850 = R1 and 190 lpmm lens = R2, you are still reduced to max. resolution of 155 lpmm to film. So I hope you are not fooling yourself thinking you can get 850 lpmm to film? For futher information, read the Fuji Film handbook. I don't want this to turn into another massive thread.

 

Bill wrote:

"I am shocked any film can resolve this high, but even so, after you run it through the 1/R formula for total camera system resolving capability, 850 = R1 and 190 lpmm lens = R2, "<p>

FYI, Minox COMPLAN R2 = 330 lpmm, wiht FUJI SUPER HR R1= 850 combined R = 237 lpmm on film.

 

Total system resolution need to include the resolution of enlarging lens.
Minox enlargement In which I tablulated the combined resolution of camera lens + film + enlarging lens
Regardless, to get the maximum resolution from Minox lens, I must use a coc of 1/330mm as a starting point.

 

There is another high resolution photographic film
www.gigabitfilm.com
A sample picture of violist Vanessa Mae by Raphael Stoetzel with Gigabitfilm
Violinist Vanessa Mae
Resolution of gigiabitfilm 720 -900 lpmm

 

Another reasonable perspective on focusing at Infinity:

Quoting Igor Yefremov:

---
Focusing at infinity should be preferred to focusing at the hyperfocal distance, only if all of the following conditions are observed:

1. There are no important objects closer than the hyperfocal distance.

2. The negatives are going to be enlarged significantly (larger than 8” x 12”).

3. The camera is installed on a tripod, and a fine-grain film is used.

If at least one of the above conditions is not observed, it is worth focusing the lens at the hyperfocal distance.

---

Reference - Search for this string:

Focusing at infinity vs. focusing at the hyperfocal distance

after linking to this page:

http://hobbymaker.narod.ru/English/Articles/sharpness_eng.htm

Mike Davis