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 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.