Does hyperfocal distance apply in large format photography when using tilts or shifts?

I just started in large format photography, and I would like to know

if I can apply hyperfocal distance focusing to maximize the depth of

field. I understand that you can use tilts and/or swings to

envision your focus plane in relation to the subject plane, because

it's how you want to visualize the field of focus. Now my question

is that can you use hyperfocal distance focusing after you make your

tilts and/or swings to further increase the depth of field? Thanks

for any response.

Using a hyperfocal distance setting doesn't maximise depth-of-field. Only stopping your lens down all the way does that.<p>All that a hyperfocal setting does is to make sure that depth-of-field isn't wasted by extending it beyond infinity. It's a bit of a ridiculous concept anyway, for anything except a fixed-focus camera.<p>There is ONE point or plane of focus, and only ONE. Everything else will gradually get more and more blurred as you move away from that plane, until it becomes unacceptably blurred, and one person's idea of acceptable focus is anothers blurry mess.<p>Using a hyperfocal distance setting is a compromise between getting near and far parts of the subject in focus at the same time, and like most compromises, it usually fails badly, with nothing in particular being in really sharp focus. Whereas, the whole point of using swings and tilts is that you can make the plane of focus pass through the most important points or areas of the subject - you don't have to compromise.<p>Briefly: No, you can't use a hyperfocal setting with swings and tilts. The two concepts are mutually incompatible.

<p>While Pete is correct in his statement about there is only one plane of focus, I don't really agree to his thougths about "acceptable focus". A shot taken at e.g. f/16 and the film lens distance can look perfectly sharp in a 8X10 enlargement, while a blow-up to e.g. 16X20 viewed at a close distance really does become the "blurry mess" that Pete says. Please note that ALL DoF scales, no matter what camera or brand is calculated for an 8X10 print viewed at one foot distance. If you intend to print a 16X20 which you expect to be viewed at close distance, you of course have to compensate for that. But if someone says that my large prints are somewhat blurry and in the process of examining the print left nosegrease marks on the print, I'd simply ignore him. I hope you get my drift here.

 

<p>To the original question: The term "hyperfocal distance" is the distance setting for getting infinity into acceptable focus, while getting something closer to the camera into focus as well. (The subject says "shifts", and shifts doesn't change the hyperfocal distance at all. I assume Alex meant "swings".) Things do indeed get more complicated when you apply tilts/swings. As you tilt the focus plane, the DoF (which with straight camera settings can be imagined as a cube.) becomes triangular in shape. If you apply both tilt and swing, that shape is somewhat like a pyramid. A good book on View Camera technique will tell you all about it.

 

<p>If I read "between the lines" in the original question, I guess that Alex wants to know if he can find the "back" and "front" of that non-cube shape through some calculation or gadget. (With a lens forward tilt, the "back" and "front" really means "up" and "down".) There are DoF calculators that are really simple to use, and they do work with tilts and swings as well. (Including free ones.) All they really do is to measure the distance from the near to far and give you an f/setting. You should set the focus exactly in the middle of near and far focus settings. All Sinar cameras since early 70-ies (F../P..) does have this gadget.

 

<p>Robert Wheeler have done a tool for handhelds (e.g. Palm pilots) that calculate most (all?) the settings you'd ever want. <a href="http://www.bobwheeler.com/photo/">Bob Wheelers photo site</a>.

Yes hyperfocal technique does have its application in view

camera work. This is the heart of most depth of field calculators

used for View camera work, whether built in (ala the Sinar

cameras or the (now discontinued) Arca-Swiss Bra inbox) or the

$35.00 Rodenstock depth of field/ tilt /swing angle calculator or

the Palmpilot version mentioned above.<P>

While is exactly right that in reality there only one absolute plane

of focus projected by a lens, stopping a lens down creates zones

of increasing distance from that one plane to achieve

'acceptable" sharpness on either side of that plane. Of course

one person�s criteria for what is sharp may differ from another�s

criteria. The limitation is that beyond a certain f-stop (say f-32 for

lenses shorter than 240mm that are used with the 4x5 format,

and f/22 for the smaller 6x9 cm format) you start to lose

resolution as light waves striking the edges of the aperture

blades diffract and interfere with the light waves directly striking

the film. (Because smaller formats need to be enlarged by a

greater degree of magnification than larger formats for the same

print size the practical limits for smaller formats are tighter. This

is also what is meant by the differing sizes of "circles of

confusion" for the various formats. But I think I have digressed for

too long.) <P> but you can see that it is important that for the best

technical quality that you don't stop down too far.<P> Here is

where the tilts and swings come into play: with your camera

zeroed (no tilts, no swings, no shifts, no rise and no fall) point

your camera directly at your subject. Determine the one best

plane to focus on usually this is near the base of the subject and

near the top of the rear of the subject. If you have one of the

calculators, determine how much tilt you need to make the plane

that contains these two points your prime focus plane. Add that

tilt to the front (lens) or rear (film) standard and refocus<P>(Yes I

know, a plane is determined by three points but ignore that or the

sake of my simplified explanation.)

If you tilt the front (lens) standard all you do are doing is

adjusting the plane of focus. If you tilt the rear standard you not

only adjust the plane of focus but you also change the

perspective rendering (the translation from 3 dimension reality to

just 2D depiction) of the subject on the film.<P>

Once this "best" plane is established you find the distance

between the nearest point you want in focus to the farthest point

you want in focus (by looking at the ground-glass) and use the

calculator to determine the f-stop you need to make an

acceptably sharp rendering -- of all of the space in between

those two points and then basically you split the difference

between how much you had to move the rear standard (I almost

invariably focus using the rear standard and not the front

standard but I use monorail cameras. For most (95%?) of the

photography I do with large format cameras this will usually

result in an f-stop in the f/22 to f/11 range. This is using

hyperfocal technique in combination with using the Schiempflug

principle (brief version of the S.P.: getting the plane of the

subject, the plane of the lens and the plane of the film to

intersect in a line.)

Yes is the short answer but look at the archives under 'technique' (where your thread is currently top of the list) for more discussions of this subject.

OK. You guys that think you can use a hyperfocal distance setting in conjunction with tilts and/or swings - How?<p>Setting the hyperfocal distance for any particular aperture means focusing at some middle-distant point determined from our chosen aperture, and whatever circle-of-confusion we decide is acceptable. Yes?<p>Now, swinging or tilting that pre-determined plane of focus through any one point of interest in our subject, may not get the focus anywhere near to where we want it to be at another point in the subject. If you follow.<br> In fact there's every chance that the swung or tilted plane will miss our chosen focus points by a mile, or at least by several metres.<br>This especially applies if our subject is close to the camera, and we're not really interested in having the horizon 'nearly' in focus.<p>So please explain to me how you can, on the one hand, focus on some arbitrary plane pre-determined by a hyperfocal distance calculation, and on the other hand, satisfy the criterion of having that focal plane pass through two or more points of interest in a subject that may not be anywhere near to that hyperfocal distance.<p>NOTE: We're not just talking about setting an adequate depth-of-field here, but about hyperfocal focussing. The two things are entirely different.

Read Harold Merklinger's books, "The Ins & Outs of Focus" and "Focusing the View Camera". You will learn all you will ever need (or want) to know about this issue.

There is a very interesting portion of Merklingers book, "Focussing the view camera", where he demonstrates with drawings how the hyperfocal distance does not change when using front tilt vs. a box camera!

Schiempflug principle and hyperfocal distance are $1000 words for a two-bit concept. I agree with Pete. I work mostly at the opposite end of the spectrum with selective focusing. for me, it is much easier to simply visualize the focus plane, and then extend that idea to a focus frame or box with depth. the box contains a gradient surrounding the focus plane that changes with aperture. our view camera affords us the luxury of moving that box, tilting the box, swinging the box, around the subject, or positioning it to encompass several subject points far removed. the key is visualizing this moving frame, know that it has a graduated depth, and identify which controls on our camera affect its orientation.

Let me add to the general confusion. Whatever the physics/optics of the situation might really be, I fail to understand how operationally hyperfocal distance can be combined with the admittedly very simple methods I use for using tilts and swings on landscape subjects when shooting typical near-far subjects. Usually the "far" part of the subject is distant enough (200 ft. or more) to count as infinity, and the "near" part is just in front of and below or to one side of the camera.

 

First method: pick two points, one distant, one close in, and fiddle with movement until both are in focus. Second, preferred method: focus on horizon (i.e. bottom of GG), then tilt or swing until near part of subject snaps into focus; then correct horizon and near focus until acceptable trade-off is achieved.

 

My question (with some of the previous posts): How is hyperfocal distance introduced into either of these procedures? Before adopting my two methods, I had previously *started* with the camera zeroed-out and focussed at the hyperfocal distance, but still ended up trying to find a compromise distance that would make both near and far acceptably sharp.

 

Again, my question doesn't concern optics but procedure.

I think the situation I had in mind for applying hyperfocal distance is where you want to get as close as possible to a foreground object that is at horizon level. If I know that the hyperfocal distance for a 150mm lens at f22 is say 40 feet (for the enlargement I have in mind) then I know that I cannot get closer than 20 feet to the subject and that the plane of focus at the horizon needs to be at 40 feet from the lens. The rest of the plane of focus can be to suit the rest of the shot.

Please don't quote Merklinger at me. The guy doesn't even know how to calculate depth-of-field properly! (Spot the glaring mistake in his article "depth of field revisited", for example. Hint: DoF is <b>not</b> symmetrical about the point of focus.)<p>OK. I've had time to think about this overnight, and the only conclusion I can reach is that hyperfocal focusing, and tilt/swing are totally incompatible.<p>Let's just think about a tilted or swung lens. The plane of focus is <i>always</i> going to have a near and a far limit. At the nearest point of focus, the depth-of-field will be shallow, and more nearly symmetrical about the focal point (ie, the DoF in front of the point of focus will be similar to the DoF behind it). Now, at the furthest point of focus, the DoF will be much greater, and will also extend much further behind the focal point than in front of it. Agreed?<br>So, what do we take as our focus point, or points, in order to use a hyperfocal ditance setting?<p>Here's a worked example:<br>Say we want to get two objects in focus; one at 3 metres from the camera, the other at 20 metres.<br>[We'll asssume a 150mm lens on 5x4 and a generous CoC of 0.14mm]<br>We <i>could</i> use a hyperfocal focus, but that would mean we'd have to stop down to f/22, and focus at around 5.3 metres, <b>and</b> it would also mean that our two objects are only <i>just</i> acceptably sharp.<p>Now we swing the lens and refocus to get both object A, and object B, in the same plane. Both objects are pin sharp this time, but consider what's happened to the depth-of-field. The DoF at object A (3 metres), again with an aperture of f/22, extends from 2 metres to 5 metres, and at object B (20 metres) it extends from 5.5 metres to beyond infinity.<br><i>Note: these distances will always be directly toward or away from the camera. Contrary to popular belief, the DoF isn't twisted by the tilt or shift. It merely varies continuously with the focal distance.</i><p>So, I ask the simple question: Where, along that plane of focus from 3 metres to 20 metres, does one take the point of reference needed to calculate a hyperfocal setting? Since, at every slice along that plane, the focus and DoF are different.<br>I suppose we could say that we don't want the DoF extending beyond infinity from our 20 metre object, and we could reduce the aperture to f/8 to rein it in, but this then means that we only have +/- half a metre of DoF at our near subject, and that almost certainly won't be enough for any practical 3 dimensional object. We end up throwing any hyperfocal calculation away, and just setting an aperture that gives us the depth-of-field <i>needed</i> by that particular scene.<p>Sorry, but I can't see how hyperfocal calculations can possibly work practically, once swings or tilts are used. Especially since it's almost impossible to set an exact pre-calculated distance on most LF cameras anyway.

The hyperfocal focusing technique (doesn't matter how good or bad is the very concept) tries to maximize focus from a certain distance till infinity. Please note: we speak about distance only: in fixed lens camera the direction is fixed (lens axis) and we may speak only in terms of distance.

 

In view cameras we have to speak in terms of distance AND direction. If a tilt/swing has been applied, the DOF zone at certain direction does already touch the infinity (and the plane of focus does it also!). Therefore the term "h. distance" is strictly speaking just irrelevant in this case.

 

What we probably can do is to recall what was the objective in that idea (maximization of sharpness zone) and to try to extend the definition of that term for the new situation. I think we inevitably have to consider the shape and orientation of the DOF zone and to decide whether a part of scene fits in this zone. It is simple and clear. I don't see how an extended concept of "hyperfocal distance-direction" is possible and how it can simplify something.

1.) Using a hyperfocus technique has <B>NOTHING to do with

focusing at "infinity".</B> neither the camera or the geometries

involved can know or hve a care about how distance theobject is

from the camera. The problem you are having comes from the

definition you are using.<P>

Pete Andrews writes: <I>"So please explain to me how you can,

on the one hand, <U>focus on some arbitrary plane

pre-determined by a hyperfocal distance calculation</U>, and on

the other hand, satisfy the criterion of having that focal plane

pass through two or more points of interest in a subject that may

not be anywhere near to that hyperfocal distance.</I><P>

Pete you are absolutely right: You can't set the camera to "focus

on some arbitrary plane predetermined by ahyperfocal

calculation." You have to focus on a plane chosen by direct

observation ofthe subject as rendereded on the

groundglass.<P> the proof that you can use a hyper focusing

technique with tilts and swings is built into the Sinar P camera

Just to clear up some misconceptions that people might be having from believing Harold Merklinger's simplistic (and wrong) view of depth-of-field:<br>Here's the correct shape of the DoF area with a tilted lens or film plane - <p><center><img src="http://www.photo.net/photodb/image-display?photo_id=857807&size=md"><p>And <a href="http://www.trenholm.org/hmmerk/HMbooks5.html">here's the way that Merklinger shows it.</a></center><p>Where Merklinger's formula of "J = f/sin(a)" comes from, I just don't know. You can see that there's no way you can fit his mythical 'J' to the correct shape of a DoF plot.

The way I like to personally look at it is that, when working with swings and/or tilts, instead of using a hyperfocal distance setting, we use a "HYPERFOCAL DISTANCE AND ANGLE SETTING." This approach is much more dynamic since (as has already been mentioned by others) we have a variable amount of DOF perpendicular to the plane of principle focus: very limited DOF in the foreground increasing to (theoretically) infinite DOF at true infinity.

 

Based upon the actual definition of "hyperfocal distance", it is accurate to say that we do not use it when we are working with swings or tilts. However, we can work with something similar to insure adequate image sharpness on all planes. Let's start by taking a look at the basics.

 

As we all know, when the film plane and lens plane are parallel, the plane of focus will also be parallel to them. If the lens plane is tilted in relationship to the film plane, the plane of focus will be tilted also. The film plane, lens plane, and plane of focus will all then intersect along a common line. These principle planes will then, in effect, radiate from this common line.

 

Once the tilt angle has been set, we can then adjust our focus setting of the lens by adjusting the lens-to-film distance. This focus adjustment will alter the placement of the plane of focus, always maintaining the common line of intersection of the film, lens, and focus planes. As the focus setting is adjusted, the common line of intersection will be relocated along the film plane, resulting in movement of the plane of focus.

 

Once we have set both the bellows extension for focus and the tilt angle, we can then stop the lens down to gain depth of field. The planes defining the near and far limits of acceptable sharpness will also radiate from the aforementioned common line of intersection, thereby giving us a wedge of DOF. As the lens is stopped down, the angles relative to the plane of focus of the planes defining the limits of sharpness will increase. According to generally accepted theory, 1/3 of the wedge of DOF will be on one side of the principle plane of focus and 2/3 will be on the other side. The planes defining the limits of acceptable sharpness will always maintain the common line of intersection.

 

Now, an expample. Say we have a pool of water in the very near foreground and a tall waterfall in the background. The distance to the waterfall is much less than optical infinity for the focal length lens we are using. This situation would probably benefit from the use of a tilt. The appropriate placement of the plane of principle focus would be at an angle running from the nearest area in the pool to a point somewhere along the vertical plane of the waterfall. The optimum angle of placement for the plane of principle focus would be such that once we have stopped the lens down, the angular plane defining the far limit of acceptable sharpness would be along the surface of the water of the pool (assuming there are no areas in the scene lying below this plane) and the angular plane defining the near limit of acceptable sharpness would lie above the waterfall (assuming there are no areas in the scene lying above this plane.) By doing this we have set both a bellows extension distance and lens tilt angle, acheiving both a hyperfocal distance setting and hyperfocal angle setting.

 

So, no, we don't work with a true hyperfocal distance setting. We work with something much more geometrically complex. At least, that's the way I like to look at it.

"Please don't quote Merklinger at me. The guy doesn't even know how to calculate depth-of-field properly! (Spot the glaring mistake in his article "depth of field revisited", for example. Hint: DoF is not symmetrical about the point of focus.)"

 

<p>Pete, you have complete misunderstoond Dr. Merklinger's result.

<p> There are two approachs to DOF

<OL>

<LI>Traditional DOF: DOF is unsymmetrical vs point of sharp focus

(page 15, The Ins and Outs of Focus )

<li> Object Plane DOF approach: the DOF IS symmetrical vs the point

of sharp focus

</ol>

You have mixed up the Merklinger's object field DOF theory with

traditional IMAGE field DOF theory.

<p> Merklinger is correct.

"Where Merklinger's formula of "J = f/sin(a)" comes from, I just don't know. "

 

<p> That means you don't have a clue what Merkligner is talking about

<p> Don't simply surf the net.

<p> Get Merklinger's "Focusing the View Camera" read it throughly

work it out, until you understand how J=F/sin(alpha), then

talk about "the guy does'nt know how to calculate DOF"

<P> Dr. Merklinger is a much better mathematician then you think

<p> BTW J=F/sin(alpha) is a correct formula

Ken, you raise some good points...and hyperfocal distance does not come into play when I use tilts. However, I would like to ask Pete Andrews something here. Pete you are one of the stronger mathematical minds on this list and I do respect your opinions, and most importantly your persistency in helping others, regardless of how bad you get attacked :-) I don't want you to think I was quoting Merklinger at you - to aggrevate you, but rather to hear your opinion on the subject. As you know, I have laid low on these lists, but I am resurfacing since I am curious of peoples opinion on this subject. First I am curious - have you studied Merklingers two books? If so, can you point out where you feel he has been mistaken. This probably should be the start of a new thread.....If someone feels compelled, please start one. I would like to share my thoughts on both Merklinger books below, as I have studied them both very extensively, unfortunately a few years back.

 

Focussing the view camera, is by far Merklingers better book. I give him this praise mainly for one reason, he wins by default. No one has tried to demonstrate mathematically the concept of tilts and swings like he has. Now, this does not mean I agree with every thing Merklinger has ever written! A fair warning to anyone who has never read his books....he is the worst writer I have experienced in my life. Although he is gifted at math, he has no technical writing skills whatsoever. You have to read his books a few times to grasp what he is trying to say...after awhile you start to understand him a bit better.

 

Now, my first question Pete.... do you accept Merklingers "J" theory? I have to admit, I feel this is Merklingers biggest contribution to tilt math. He has developed a very simple way to determine where the plane of sharp focus will interesect under the lens. In situations where this is known, which is quite often, (or always if you are good at sketching geometry) this completly simplifies the tilt angle required. I have tested this for years - and all the frustrations I have faced with this books, well, this one concept makes it all worth while. Now, his other contributions towards view camera math are either less important or more complicated, at least in my opinion.

 

When using front tilt, setting the tilt angle is by far the most important ingredient...get this wrong, and everything that follows will be wrong, it is clearly the starting point. Next is the focus distance, (which sets the angle of the plane of sharp focus) which Merklinger demonstrates mathematicaly...but considering how hard it is to focus the rear standard with mm numbers, it is very impractical in the field. You must know the lens nodal distance for each lens, film position, etc. So this is more easily accomplished via the gg and a few seconds of trial and error with the back focus. And if you set the tilt angle right, it works quite easy. The only other issue with tilt is making sure the DOF above and below the plane of sharp focus meets the needs of the scene.

 

Merklinger demonstrates a way to determine the DOF above and below the plane of sharp focus at a specific distance, when using front tilt. He demonstrates DOF as being x number of J's above and below the plane of sharp focus, at a specific distance from the lens. This I have not seen demonstrated by others and can be quite useful. However, its not always a simple thing to determine, and more importantly, sometimes following his calculations, and bringing such to the field, my results do not always match perfectly....but, they are not off by much, which is somewhat comforting. (I would not doubt I have erroed at times also) So overall, I would offer Merklinger has defined mathematically the 3 most important aspects of tilt, angle, focus and DOF as well as anyone, although the most poorly written!.

 

His contribution towards Hyperfocal distance and view camera, is very complex, and the example Pete showed us above is not the whole story. But by no means would I want to try to address this in a thread such as this. I personaly don't see why Merklinger attempted this, as there is little importance or significance between conventional Hyperfocal distance with non tilt cameras and vs. tilting applications.... But I will mention, all Merklingers J calcs and DOF calcs when using tilt, involve the use of the Hyperfocal distances of the lens for the completion of his formulas. I could go on about other topics for view cameras in his books, but I feel these are the key ones. I would love to hear from others on this.

 

Now, here is the scary part. In Merklingers book, The Ins and outs of foucs, he discusses an entirely new concept of DOF which defies DOF calcs that has been around for hundreds of years. (this is for non view cameras only) He assumes the time tested DOF formulas are wrong today, as they were developed in times when there was very poor resolving lenses and films - 150+ years ago. He backs all of his tests / views up in his book with photos....He also disproves conventional DOF calcs with photos. Although his concept in some situations appeals to my common sense, overall, I feel his radical concept is totaly flawed. I think he may have been using a camera with a faulty alignment between film / lens / miror. He took all those pix with 35mm SLR. It's very possible, he may have tricked himself on this one. I have done several tests to be sure he is wrong.... and I am convinced his theory is flawed. Many others concur with me. But in a case like this, I doubt the author would ever come out and admit a book that is currently on sale at many retail outlets is flawed. This is unfortunate as there is not a lot of books written soley on DOF or focus.. so there is parade of newcomers who may be mislead by this book.

 

I guess what I am getting at...and hopefully other Merklinger proponents or opponents will respond. If you read his flawed book first, and you discover these flaws yourself, you tend to be immediately anti Merklinger. The ol adage,, "throwing the baby out with the bath water" applies here.... but if you objectively make your way through his view camera book, I think you will find he does have some excellent concepts which have been explained like no one else up to this point in time. It's too bad the one book dedicated to the math and concepts behind veiw camera tilt, consist of near impossible technical reading, a flawed second book, and many opponents. But rarely do I see anyone attempt to technically disprove his fundamental concepts - i.e. the 3 ingredients of tilt that I mention above. Does this make sense? Pete, or anyone else that can provide such data should present it. This type of post shoud be archived on the home page as tilt is one of the most important aspects of using a view camera and Merklinger keeps getting new readers every year, and his proponets probably equal his opponents. But rarely is their positions clearly defined. There has been many threads on this in the past.....

 

 

 

 

Bill

<p> Your assesment of Merklinger's J theory is correct. It is his

most important contribution to view camera photography

<p> You still haven't got the essense of his Object Field DOF theory

It is not flawed at all.

There is a thread about Merklinger's Object field DOF theory

in Leica Photography, where I provided a table, demonstrating why

focusing at infinity instead of focusing at conventional hyperfocal

distance yields sharper landscape pictures

 

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

Focusing Leica: Merlinger Method </a>

Martin, I read the thread. I should have been more clear....it has been awhile since I read this book. Focussing at infinity vs. the hyperfocal distance.... that is one of the items I would not dispute. I was referring to his discussions on fouccussing on closer objects. The way he uses an inverted X to demonstrate focussing on closer subjects is where I found major flaws. My results did not concur with his. I have had several DOF gurus also concur with this. I wish I had more information, but it is all burried in a box right now. However, I apologize for lumping everything in the book together.when I made my comments.

At least we now know why the good doctors' nickname is Murky

Merklinger. <P>Anyone who makes something simple so

complicated deserves to be ignored. I'm completely with Pete on

this. merklinger is one of those people who make it impossible

for people to concentrate on the important thing in photography:

seeing. His jargon is so dense that even Sir Stephen Hawking

and the late Richard Feynmann would be stunned into silence

and Ansel Adams, John Sexton, Norman McGrath and Richard

Avedon would have thrown away their cameras in djsgust.<P>No

doubt his mathmatical explanation is correct, but learning to use

a view camera his way is like having to do all of the engineering

of tires, brakes, steeering, axles, transmission, motor, electrical

systems, chassis construction and paint technology each time

you wanted to go for a drive in your car.

"Here's a worked example:

Say we want to get two objects in focus; one at 3 metres from the camera, the other at 20 metres.

[We'll asssume a 150mm lens on 5x4 and a generous CoC of 0.14mm]

We could use a hyperfocal focus, but that would mean we'd have to stop down to f/22, and focus at around 5.3 metres, and it would also mean that our two objects are only just acceptably sharp.

 

<p> Comment: You have transplated the DOF concept in tiltless camera

to camera with lens tilt. <p>

Now we swing the lens and refocus to get both object A, and object B, in the same plane. Both objects are pin sharp this time, but consider what's happened to the depth-of-field.

 

<p>Comment yes, the first step is to use lens tilt to get object A and B on PLANE OF sharp focus. But that is not all. <p>

 

 

The DoF at object A (3 metres), again with an aperture of f/22, extends from 2 metres to 5 metres, and at object B (20 metres) it extends from 5.5 metres to beyond infinity.

 

<p> Comment :That is where you get it all wrong, you are using 35mm math here.

 

<p> The near DOF limit and far DOF limit are not planes perpendicular

to point A and point B. Rather the the DOF limit planes are like V shape, with the PLANE OF sharp focus still PASSING through A and B

such that they are tack sharp. This plane of sharp focus is approximately dissecting the V shape. <p>

<p> Take a simple case, if point A and point B lies in a flat field

point A is a small flower, at point B is not a small flower, but a

statue of certain height.

<p> If you use lens tilt to bring the small flower at front and the

FEET of statue into PLANE OF SHARP FOCUS, then the head of statue would

not be sharp.

<p> The right way to do is draw a slant line from the small flower (point A) to the MIDDLE of the statue, point C, select lens tilt to

bring point A and point C into PLANE OF SHARP FOCUS.

<P> Then select proper aperture, according the tables in Merlinger's book, such that near DOF limit plane passes the hinge point at one end and

the HEAD of statue at the other; the far DOF plane passes the

hinge point and the FEET of the statue. Now you get not only

the front object: small flower sharp, you get the HANDS of statue

tack sharp, but also the statue HEAD and statue FEET within DOF

That is how dof comes into play when lens tilt is used

"Where Merklinger's formula of "J = f/sin(a)" comes from, I just don't know"

 

<p>It is implicit in Fig 22 of "Focusing the View Camera"<p>

 

In that diagram, three lines

intersect to form a right angle triangle:<p>

 

<ol>

<li> Optical axis passing through the center of lens

<li> Front focal plane

<li> Parallel to film plane, acronym PTF plane, ie a plane which

is parallel to the film plane AND passing throught the center of lens

</ol>

<p> focal length f is the short side of right angle triangle

<p> J = lens to hinge distance is the hypothenus

<p> Front focal plane and PTF plane intesect at the Hinge line

<p> The angle between the front focal plane and PTF plane is alpha

<p>

Therefore SIN (alpha ) = f/J

<p> and J = f/sin(alpha)

<p> This is quite elementary.

 

<p> The information on the Merklinger website is only a brief summary

of what was discussed in depth in the books