patrick_chase

Hi Rob;

<p>

If it's a 90 f/8 (you didn't specify the F.L.), and you shoot slide

film, and you plan to use substantial movements, then the answer is

probably "yes".

<p>

I have a Nikkor SW 90/8, and I found that there was little falloff on

4x5 when the lens was centered w.r.t. the film, but that the falloff

got more dramatic (up to ~1.5 stops) when I used extensive movements.

I ended up getting a Heliopan 1.5-stop center filter to correct the

problem.

<p>

I'd like to throw out a couple corrections:

<p>

1. It is very important to distinguish falloff from vignetting: They

are completely different animals. Vignetting is what happens when you

exceed the coverage of one of more elements in the lens

(typically the front or rear elements, since they are often a bit

undersized). Vignetting occurs only near the coverage limits, and

typically decreases as you stop the lens down. Wide-angle falloff is

more uniform in character, and is not affected at all by aperture.

<p>

2. Bob Salomon writes that "All modern wide angles have similar fall

off". This is decidedly untrue. The exact optical layout of a lens has

a significant effect on falloff. In particular, use of strongly

negative front and rear elements reduces falloff by causing the

entrance and exit pupils to "swing" as the angle of incidence changes.

The catch is that strongly negative front and rear elements tend to

cause aberrations, so the designer must balance sharpness vs. falloff.

Before anybody mentions "cos^4", it should be pointed out that the

cos^4 law only pertains to the idealized thin lenses of optical

theory; Modern wide-angles are anything but "thin lenses"

<p>

-- Patrick

Voightlander made a lens called the "zoomar". Could that be what Sean

refers to (it had a horrible reputation, IIRC).

<p>

-- Patrick

Hi Bill;

<p>

Are you dividing by the enlargement factor squared?

<p>

Line pairs per millimeter is a linear measure of resolution (i.e. it

measures resolution along a single axis rather than the amount of

information contained per unit area), so an LF original with 56 lp/mm

of "perfect" resolution (i.e. MTF is close to 100% all the way out to

the 56 lp/mm limit) would produce exhibition-quality results when

"perfectly" enlarged up to 8X (=56/7), or ~32" x 40".

<p>

There are two catches though:

<p>

1. Stated lens resolutions are usually the perceptible resolution

limits, which typically exhibit MTF in the 10-20% range, if that. The

oft-applied Rayleigh criterion for diffraction-limited resolution

yields about 18% MTF at the calculated limit (of course, the Rayleigh

criterion also assumes point sources, so it's open to question whether

it's really applicable to this discussion at all).

<p>

2. Enlargement is _never_ perfect (though with modern techniques it's

getting pretty close!).

<p>

Regards,

<p>

Patrick

Hi Joe;

Textured detail as seen in feathers, fabrics, and the like is most visible when illuminated by directional sidelighting. Low-contrast conditions typically imply nondirectional lighting (for example, uniform overcast or open skylight), which is about the WORST thing you can have if you want to reveal texture in your subject.

Regards,

Patrick

Hi All;

<p>

Great thread!

<p>

One apology/clarification: Glenn Kroeger rightly points out that I got

my estimates of diffraction-limited resolution wrong. Specifically, I

used a relation (the Rayleigh criterion) which is specific to

resolvability of adjacent point sources, and the way I used it to

estimate the continuous (i.e. non-point sorce) case of an MTF target

was very pessimistic. All that I'm really sure of now is that the real

diffraction-limited resolution numbers are somewhere between what I

posted and double what I posted.

<p>

Sorry about the confusion!

<p>

-- Patrick

Hi John;

Why not a set of Kinesis or LowePro Street&Field cases? (my personal choice would be is Kinesis, both because I think they're better bags, and because LowePro appears to have ripped their designs off shamelessly - http://www.kinesisgear.com/)

You can lash either to the webbing of your backpack when you're hiking in and out, and then put them on their dedicated harness or belt (which you would presumably carry in your backpack) when you're actually using them.

This is a reply to Bill Glickman's comments:

<p>

In my experience, resolutions higher than about 60 lp/mm are pretty

much mythical beasts in ANY film format. One reason already pointed

out is the resolution of the film itself. A second is the fact that

diffraction typically ends up limiting you to far less.

<p>

Let's look at that "140 lp/mm" Mamiya lens that Bill raves about as an

example: Simple theory and a bit of math tells us that such resolution

is only obtainable at apertures of f/4.5 or wider even if the lens is

otherwise perfect in all respects. By f/8 you're limited by

diffraction alone to about 85 lp/mm, and at f/22 (a reasonable opening

for near-far lanscape shots in 6x7) you're limited to 57 lp/mm. All of

a sudden the pathetic-sounding 50 lp/mm resolution of that Nikkor M

(or Danny's Fuji, which is a pretty similar lens) begins to look like

it might really be a non-issue after all. At the f/45 opening that

Danny used in his test, the diffraction-induced resolution limit is

about 30 lp/mm. He'd might as well have been using a Wollensack or a

polished Coke-bottle bottom at that point.

<p>

Furthermore, the human eye is only sensitive to spatial frequencies

out to about 7 lp/mm (and even that's rather optimistic for anybody

over age 30), so I seriously question Bill's ability to perceive

anything past ~50 lp/mm through an 8X loupe. I know I can't (I've

tested myself and others using targets of known frequencies as part of

my job).

<p>

Bill, if you can see a significant difference between your 6x7 chromes

and 4x5's shot with lenses as good as the Super Symmar under an 8X

loupe, then I respectfully submit that there is something wrong with

either your equipment or your technique. Well-executed LF work with

top-notch lenses at ideal apertures should be nearly indistinguishable

from perfection under magnification that weak, so no matter how good

the Mamiya system is, the differences shouldn't be anywhere near as

dramatic as you imply. Critical examination under a quality microscope

might be another story altogether, of course...

Hi Dan;

I just realized tonight what caused the specific problem where the EOS 3 failed to focus on a heron's neck. The 100-400IS is a slow lens (f/4.5-5.6 to be exact), and the EOS 3's horizontal AF arrays only work with fast lenses (f/4 or faster for the center sensor, f/2.8 or faster for the other cross sensors). Thus, when used with the 100-400, the EOS 3 is only sensitive to horizontal edges when the camera is in landscape orientation. A neck presents mainly vertical edges, which explains the camera's tendency to grab other scene elements.

IMO the lack of cross sensors which work with slower lenses is one of the more crippling liabilities of recent EOS bodies, compared to their competitors.

-- Patrick

Hi Dan;

Is the AF point directly over the bird lighting up when you do this, or is the body telling you that it's finding focus elsewhere? Also, have you checked to make sure that CF17 hasn't been set to 1 or 2? Either of those settings would cause the body to use a cluster of sensors to form a larger AF "sweet spot", which could in turn cause it to pick up the background instead of a small foreground subject.

I second Bob's suggestion that you try selecting a single AF point manually if you haven't done so already. I've never seen a camera from ANY manufacturer that I trust to pick the correct AF zone for me.

Finally, it's probably worth noting that I my EOS 3 consistently focussed ever so slightly in front of its subject when I first got it. A quick visit to the friendly neighborhood Canon service center (fortunately located a bit over an hour away) for realignment fixed the problem.

A comment to Sean Yates: I'm not sure I see why the existence of the

Technikardan in particular should have any effect on the market for

yaw-free, base-tilt only cameras like the VX-125 or the Cambo. The

Technikardan is a non-yaw-free, center-tilt camera, just like many

others on the market (though it's arguably far better built than

most...). People who like center tilts will buy the Technikardan and

cameras like it, just like they always have. People who like yaw-free

base tilts will buy yaw-free base-tilting cameras, just like they

always have.

<p>

The cheapest way to get a camera that does both yaw-free base tilts

and center tilts is either the Linhof Kardan GT45, or the Arca-Swiss

F-line with the optional Orbix (both of which run in the low $3000s,

though I'm not positive about the price of the Orbix).

<p>

-- Patrick

<p>

-- Patrick

Hi;

<p>

I've moved the (tangential) discussion of perspective manipulations

into its own thread because it really doesn't belong here...

<p>

Thanks,

<p>

--P

Hi;

<p>

This is a continuation of a tangential discussion from the "Pros and cons of field cameras" thread. In that thread, I wrote:

<p>

"Consider the simple manipulation of using front rise to prevent convergence. Convergence is a perspective effect, and front rise can be used to control convergence. This example therefore proves that camera movements CAN alter perspective. Obviously, there are some limitations: In particular, camera movements cannot alter the near/far size relationships of objects which are overlapped in the image (though you CAN alter the aparrent size relationships of objects which are separated in the image...)"

<p>

Larry Shearer then replied:

<p>

"Not that I am trying to cause more confusion for Alan then is already present,but Patrick how do you control convergence of a scene by raising the front standard? Alright I have to drop a name here

e,ummm Ansel Adams states on more than once in "The Camera" that "True perspective depends only upon the camera-to-subject distance." (page 106)."

<p>

Depends on what you define as "perspective". When Ansel Adams says "perspective", he is defining it as the size relationship between near and far objects which overlap in the scene. He's right, but only within the narrow limits of his own definition. To see where that definition breaks down, consider the following example: You have a near object on the left side of the image, and a far object on the right. You want to change the relative sizes of those object without moving the camera. Though Adams' comment appears to suggest that you cannot accomplish this task, it is in reality a very simple matter of swinging the back standard such that the film plane moves away from the object you want rendered larger (you'll then probably need to swing the front standard as well to establish focus). The reason this works is because changing the relationship between the film plane and subject planes allows you to change the distance relationships between off-axis subjects, the lens, and the film plane without moving the camera. The key thing to note here is that for this trick to work, there has to be separation in the image between the objects whose relative sizes you are trying to alter. If they're overlapped, then you're hosed.

<p>

Whether you call what I've described above "altering perspective" or not is entirely a matter of semantics.

<p>

Just to be perversely confusing, I'll also throw out a case where camera movements truly cannot alter perspective: When photographing with a fisheye lens.

<p>

To understand the answer to your specific question about correcting convergence, you need to understand how rectilinear lenses work: A rectilinear lens renders parallel lines in the subject as parallel in the image if and only if those lines lie in a plane which is parallel to the film. To use movements to eliminate convergence, you simply set the back of the camera parallel to whatever it is you're photographing (for example, the side of a building) and then use rise/fall and shift to establish the composition you want. Note that what I've described above controls covergence on both the horizontal and vertical axes; If you're only worried about one or the other, then you only need to set the film plane parallel to the subject along that one axis. Adams definitely explains this to some degree in "The Camera".

<p>

You might want to check out the Stroebel and Simmons books (Stroebel is encyclopedic; Simmons is more readable) on large-format technique.

<p>

-- Patrick

fw wrote thusly:

<p>

"One last thing - the movements on the camera do not control

perspective, they enable you to control where a plane of sharpness

will lie in the image. Only physically moving the camera to a

different location will alter the perspective of the image"

<p>

Consider the simple manipulation of using front rise to prevent

convergence. Convergence is a perspective effect, and front rise can

be used to control convergence. This example therefore proves that

camera movements CAN alter perspective.

<p>

Obviously, there are some limitations: In particular, camera movements

cannot alter the near/far size relationships of objects which are

overlapped in the image (though you CAN alter the aprrrent size

relationships of objects whicht are separated in the image...)This is

probably the specific case that fw was probably thinking of.

<p>

-- Patrick

Hi Doremus;

<p>

Julian's web page says "scale focussing", which implies that you focus

by estimating the subject distance and then racking the focussing

mechanism in or out until the focussing distance scale tells you

you're focussed in about the right place.

<p>

-- P

Hi;

<p>

I think that there's a serious lack of accuracy in this thread

regarding effects of filmplane to groundglass misaqlignment.

<p>

One poster has stated that the effects are worse for long lenses than

for short; Another has stated that they are worse for short lensesthan

for long. In truth, NEITHER is right.

<p>

For a traditional (i.e. non-tele, non-retrofocus) lens the f-number is

defined as the ratio of focal length to the exit pupil diameter. eaqch

individual point in the image is formed by a cone of light, the base

(wide part) of which is at the exit pupil, and the point of which is

at the film plane. When the GG and film are misaligned, the film isn't

positioned at the point of the cone, and points in the subject are

therefore rendered as discs in the image. The diameter of these discs

follows trivially immediately from the definition of the f/number:

it's simply

<p>

blur_diameter = defocus_distance/f_number

<p>

That's all there is to it. The focal length of the lens is utterly

irrelevant. I'm sure that these myths will return by next week, though

;-).

<p>

-- Patrick

A few clarifications:

<p>

1. I'm not the person who posted the URL for the Polaroid data sheets,

but like Daniel I'm eternally grateful to the person who DID do so...

<p>

2. The groundglass on both my Linhof Color Kardan and on my Arca Swiss

F agree closely with all of my conventional Fidelity and Lisco

holders, so I don't think that the cameras are the problem.

<p>

3. What originally prompted my post is that I noticed that Type 55

negs and Quickloads shot at even moderate apertures (for example,

f/16) with my 545i were somewhat blurry. Further testing revealed that

this combination consistently focusses in front of the intended plane

of focus.

<p>

4. I measured the flange-to-film distances of my Polaroid 545i holder

and a known-good Fidelity holder with a runout gauge. The Polaroid

holder places the film ~0.5 mm further back than does the Fidelity

holder, which is consistent with my previous observation that the

plane of sharpest focus is closer to the camera than intended (1/i +

1/o = 1/f and all that...)

<p>

I'm currently getting decent results by displacing the back standard

forward 0.5 mm after focussing when shooting with the Polaroid holder,

but that's a very inconvenient solution (and one which defeats the

entire point of using Type 55 negs to check focus...).

<p>

It sounds as though my 545i sample may be defective, so I'll take it

up with Polaroid. Thanks for all the feedback!

<p>

Regards,

<p>

Patrick

Hello;

<p>

Has anybody here tried exposing (NOT developing) Polaroid Type 55 in a Fuji Readyload holder? Did it work?

<p>

The reason I'm asking is that I'm REALLY getting sick of the Polaroid 545i's incorrect film plane position (the back plane of the holder is about 0.5 mm further from the flange than in my Fidelity holders, and focus in the final exposure is shifted by about that much relative to the ground glass on my cameras) and inability to hold the film flat. It's worse than useless, and I'm just about to the point of giving up on Polaroids altogether unless I can find a better holder.

<p>

I've heard that the Fuji is better in both regards, so I'm thinking that might be a solution?

<p>

Thanks,

<p>

Patrick

Hi Craig;

I've had mine for a bit over 2 years of moderate use (I'm a weekend warrior, not a pro), and if anything it's a bit less stiff than when I got it. That having been said, I've taken the following precautions to keep it that way:

1. The head stays safely in my backpack during prolonged periods of non-use

2. When it's on my tripod and not in use, the head is ALWAYS covered by a pouch.

3. I clean the ball with rubbing alcohol (as recommended in the instructions) fairly frequently.

If the head you're looking at is really stiff, then it's probably not worth going for.

Regards,

Patrick

Regarding Michael Biggs' comments about light falloff: The cos^4 rule

is derived from thin-lens theory, and isn't necessarily a very good

predictor of the behavior of real lenses. The Nikkor SW designs in

particular seem to "swing" the entrance pupil around a bit, which

reduces the light falloff to below what the cos^4 rule would predict.

I measure between 1.5 and 2 stops of falloff at the edge of my SW

90/8, whilee cos^4 would predict a bit over 3.

<p>

-- Patrick

Hi Paul;

<p>

I'm intrigued by your comment about being "somewhat limited on my

favorite long lenses" with a monorail. The Technikardan has a maximum

extension of 48 cm (19"), which is more than a Technika, so I can't

see where you'd be liomited there.

<p>

The Arca-Swiss F-line's maximum extension is somewhat limited in its

default configuration, at 38 cm (15"), but can be inexpensively

upgraded to provide a maximum extension of 60 cm (23.6") by replacing

one of the 15 cm monorail segments with a 30 cm part, and by adding a

long bellows (with the F-line Compact you'd want to add the 25 cm rail

extension II instead, which would bring the max. extension to 55 cm).

<p>

-- Patrick

"Astigmatism" is an optical aberration wherein the tangential and

sagittal axes of a lens focus on different planes. Consider the circle

of coverage of a lens. Now imagine a point near the edge. If you draw

a line from that point to the center, then that's the sagittal axis. A

line perpendicular to the one you've just drawn would be the

tangential axis. In a lens with a lot of astigmatism, you can focus

sharply on modulations along the sagittal axis, or on modulations

along the tangential axis, but not on both at the same time. In

practice, unless the astigmatism is REALLY bad you can usually work

around it by stopping down to small apertures.

<p>

An "anastigmat" is simply a lens which is corrected for astigmatism.

Almost all modern LF lenses are pretty well corrected for astigmatism,

though many older ones aren't. Back when some were and some weren't,

the makers differentiated the ones which were by calling them

anastigmats.

Hi Mike;

I think that a lot depends on what you shoot. For wildlife shots in general, and for "fast-breaking" applications like birding in particular, I can't imagine using anything but a modern 35 mm SLR.

On the other hand, my personal experience is that view cameras reign supreme for landscapes and scenics, both because of the larger film size and because they allow manipulation of both perspective and focus via movements (note that "view camera" doesn't automatically imply large-format: Many MF view cameras are available). I personally don't have much use for MF cameras which don't allow movements, but I know many who would disagree...

-- Patrick

Hi Rob;

<p>

Given the set of simultaneous requirements that you've listed, and

your aversion to excess weight, I think that your budgetary

expectations may be a bit unrealistic.

<p>

I doubt that you're going to do much better than the Arca-Swiss 5x7

that Ellis suggested. No other similar-weight or lighter 5x7 on the

market meets your specific set of requirements (the bit about fully

independent movements in particular rules out the otherwise promising

Sinar f1/f2 because they uses combined tilt/swing locks). The Linhof

system that Bob S recommends is also excellent (choosing between it

and the A-S would probably be a matter of individual working style),

but will cost you as much as or more than the A-S, so you're not going

to save any money by going that route.

Hi Darron;

<p>

"Noise floor" is a commonly accepted term for what you were trying to

describe in the image capture world.

<p>

High-end drum scanners use photo multiplier tubes as their capture

elements. PMTs have inherently superior noise performance compared to

CCDs for any given level of sensitivity (scientific CCDs do have very

good noise performance, but their sensitivity is low, so you really

have to blast them with light to attain full saturation with a

reasonable line period).

<p>

That having been said, there are CCD-based scanners on the market

which offer extremely good noise performance. I've had a few 4x5's

scanned on a CCD-based Scitex flatbed recently, and the results were

good enough that I frankly can't see any reason to drum-scan them. Of

course, the Scitex in question is a $50K scanner, so it's really not

any cheaper than a drum.

To Bob Salomon;

<p>

You might note that I said "using" instead of "fitting" in my post. I

did that for a reason ;-).

<p>

Given that my LF experience is with a Linhof Color Kardan (uses

Technika boards, just like Daniel's TK) and an Arca-Swiss F 4x5 with a

Technika adaptor, I'm _quite_ well aware that you can get Tech boards

for all common shutter sizes, and that the main issue is getting the

rear of the lens through the hole in the front standard. The reason I

didn't state that is because I felt that you yourself had done such a

good job of explaining the issue in your initial post that it didn't

bear repeating.

<p>

An aside: I DO know one guy who's crazy enough to take his lens apart

and reassemble it around the front standard with the bellows detached

every time he want to mount it...

<p>

--P