Apo-Grandagon & f-stop

[Emre Yildirim]

I have a really basic question:

Some lenses only cover 4x5 at a larger f-stop, i.e. my newly purchased 55mm Apo-Grandagon has an image circle of 163mm at f/11. Obviously, shooting at f/16 or f/22 will not increase the image circle or affect the light falloff on the edges in any way.

The working f-stop according to the documentation is f/8-11, which is smaller than what I usually use with regular lenses. I'm guessing the lens is sharpest at f/8-11. I want to get the sharpest possible images, but I'm worried that shooting at f/8 or f/11 will not give me enough depth of field. Is the DOF visually the same at f/11 on a 55mm lens as, for example, a regular 180mm lens at f/22? This might be a stupid question, but I'm actually very curious whether DOF is somewhat different with very wide lenses, as the widest I've shot so far is 72.

(note: I haven't done any shooting yet, I'm still waiting for a recessed lensboard to get here.)

[Dan Fromm]

There are many on-line depth of field calculators. Google will find them.

[Ron Marshall]

Here is a good dof calculator:

http://bobatkins.com/photography/technical/dofcalc.html#calc

[Emre Yildirim]

Ron, that was big help. Looks like I won't have to worry about DOF & small f-stop with that kind of focal length.

[Steve Hamley]

Emre,

To answer your question qualitatively - and I use a 55mm Apo Gandagon - you will rarely have to shoot at an aperture smaller than say f:16. If you want to see what the DOF is like, just put a 50 or 55mm lens on a 35mm camera, The DOF will be the same.

Depending on what camera you use with what bellows, you'll also have (rear) movements available to help out. You won't need much.

Steve

[Eric Brody]

DOF is relative. It depends on the defined "circle of confusion," an apt term. The circle of confusion is different for different films sizes and is somewhat arbitrary. One scale I have seen uses .03mm for 35mm, and 0.20mm for 8x10 with 6x6 @ 0.45mm and 4x5 @ 0.1mm. Therefore, the depth of field may not be estimated by looking at a 50mm lens on a 35mm camera.

[Ralph Barker]

I have an HTML-based DOF calculator (http://www.rbarkerphoto.com/DOF2.html) on my site that was originally written by Michael Gillett.

As Eric pointed out, different people use different values for the CoC used in the calculation. Mine is based on the following Circle of Confusion sizes (in mm): 35mm = .025, 645 = .043, 6x6 = .049, 6x7 = .053, 6x9 = .062, 4x5 = .094, 5x7 = .126, 8x10 = .188.

If you want to modify the CoC, do a "view page source", cut and paste the text to a local file, and change the CoC values to what you want. I have permission from Gillett to display his code, but if you put your modified version up for public use, you'll need to contact him separately for permission to do so.

[Steve Hamley]

Just curious here, but I never mentioned film sizes. Am I missing something re: "seeing" what the DOF looks like? To imply the DOF looks different to your eye through a 55mm lens for 35mm format versus looking through a 55mm Apo Grandagon would seem to imply something changes in your eye, right?

Steve

[Bob Salomon]

"The DOF will be the same."

At the same magnification. But you use less mag. on 45 normally so it won't be the same as on 35mm.

[Jerry Fusselman]

People using larger formats usually choose a larger circle of confusion, for several reasons (including magnification for printing). However, Steve's statement is correct that the depth of field is format-size neutral if you hold focal length, aperture, and circle-of-confusion size constant across formats.

[Bob Salomon]

"format-size neutral if you hold focal length, aperture, and circle-of-confusion size constant across formats"

And magnification. The greater the magnification the less apparent sharpness at the extreme ranges of the dof.

[Jerry Fusselman]

Hi Bob,

By "magnification", you mean "print magnification" as I understand, it because you earlier wrote "you use less mag. on 45 normally," I hope we (like everyone else in this thread) are agreeing to hold focusing distance constant as we vary the film format and that we are assuming an ideal lens. I hope you also agree with customary usage that circle of confusion refers to a distance measured on the film and not the print.

I take your "and magnification" statement to mean that my math was wrong and that I should have included print magnification in my list of crucial variables that affect depth of field. If this is not what you meant, I apologize, and maybe you can clarify. If this is what you meant to convey, it is wrong. It is a fairly common error. I will try to show this in three ways:

1. There are no decent depth-of-field-calculation programs that have inputs for both circle of confusion and print magnification if the other variables are focal length, aperture, and focus distance.

2. There are no decent depth-of-field formulas that include both circle of confusion and print magnification if the other variables are focal length, aperture, and focus distance. For example, Jeff Conrad's recent articles determine depth of field using N, f, c, and u, which relate to aperture, focal length, circle of confusion, and focus distance. That's all you need---there is no need for variables of print size or format size.

Now if that seems like it cannot be right, maybe it will help if you think of film size and print size determining c.

3. Imagine focusing at 100 meters with a 55mm lens at f/11 with a circle of confusion of 0.1mm. That determines your depth of field, as you can see in Jeff Conrad's figures and formulas or with decent depth-of-field-calculation program. You can assume a 4x5 film size if you like, and you can assume an 8x10 print if you like, but the depth of field is unaffected by these choices. You can change your mind and ask for an 80x100 print, and you still have the same depth field---unless you change your circle of confusion.

So depth of field is indeed format-size and print-size neutral if you hold focal length, aperture, focusing distance, and circle-of-confusion size constant across formats.

Of course, many photographers don't hold circle-of-confusion size constant across formats, which is just what I said in the first sentence of my original post.

This way of looking at it---having c as a single variable instead of format size, print magnification, viewing distance, personal taste, subject matter---seems better, becuase you get a definitive range for your depth of field.

[Bob Salomon]

Jerry,

Think of the DOF preview on a 35mm SLR. If you use it to preview it is only accurate at the same effective print magnification as the magnifier in the finder. Make a print with more enlargement and the dof will not be what you saw in the finder.

The Rodenstock DOF calculator lets you dial in film size which is really changing the CoC without worrying or needing to know what CoC is.

We recommend that you always dial in a smaller film size then you are shooting if you will be blowing the shots up very much. That way the DoF is narrower but holds up to enlargement better.

[Jerry Fusselman]

Bob,

I cannot tell your position. It would be nice if we could agree so that we don't give out false information. Do you now agree with the following sentence?:


Depth of field is format-size and print-size neutral if you hold
focal length, aperture, focusing distance, and circle-of-confusion size
constant across formats.

If you do not agree, I would be delighted to see your formula for depth of field that includes both circle of confusion and print magnification! Again, I expect that you can find no such formula. If you do agree with the quoted sentence, then your correction of my statement listing the variables affecting depth of field with "And magnification" you now realize was a mistake on your part.

That people change their CoC when they go to different formats I have admitted more than once----including my first sentence in this thread, which was this: "People using larger formats usually choose a larger circle of confusion, for several reasons (including magnification for printing)." So of course I do not dispute your last two paragraphs just now. (However, the first paragraph in your most recent reply I disagree with, because I find Merklinger's analysis of this issue convincing, but DOF preview is a red herring for the issue we have been discussing.)

Again, depth of field can be found with just four variables: focus distance, aperture, focal length, and circle of confusion. As a statement of mathematics, you don't need to know anything else. Your assertion that I should have listed magnification too is false, because circle of confusion is one the variables in the initial list. Do you now see this?