Larger image circle = more DOF? (same focal length, format, aperture, distance)

[jvanhuys]

Morning everyone and happy Friday!

There are two 210mm lenses available to purchase for my 4x5 camera. One has an image circle of 250mm and the other has 400mm. I'm curious if I would get deeper/ more/ wider depth of field from the larger image circle lens, when I have the exact same shooting parameters, namely:

- f/22
- 2m subject distance

I appreciate your time. Thank you!

[Bob Salomon]

No.

[jvanhuys]

No.

Cheers for the response Bob. Appreciate it. I was under the impression larger image circle also means larger 'circle of confusion', which affects depth of field?

I'd appreciate any further elaboration you can provide.

[Bob Salomon]

Cheers for the response Bob. Appreciate it. I was under the impression larger image circle also means larger 'circle of confusion', which affects depth of field?

I'd appreciate any further elaboration you can provide.
Circle of confusion depends on how large a print you want and what aperture you use.

[Alan Klein]

Circle of confusion depends on how large a print you want and what aperture you use.

Bob, I think the OP's question is the relationship between the image circle and the circle of confusion?

[Kiwi7475]

Read this

https://www.largeformatphotography.info/articles/IntroToDoF.pdf

More image circle in excess of the target film size allows you to move the film around to help composing but whatever is in excess of that area doesn’t hit the film or the ground glass other than creating stray light potentially bouncing inside the camera (which can sometimes be detrimental to image quality). But it has no relevance to the COC or DOF.

[xkaes]

You are not the only person confused about the circle of confusion. The COC is changed by the f-stop and the size of the negative, but not by the size of the image circle created by the lens -- assuming you are using the same film format.

IF you have a lens with a large IC, the COC will be different if you use 4x5 vs 8x10. With the 8x10 film you don't have to enlarge as much, so the COC is "better".

[xkaes]

You are not the only person confused about the circle of confusion. The COC is changed by the f-stop and the size of the negative, but not by the size of the image circle created by the lens -- assuming you are using the same film format.

IF you have a lens with a large IC, the COC will be different if you use 4x5 vs 8x10. With the 8x10 film you don't have to enlarge as much, so the COC is "better".

Getting a lens with a larger IC will only improve the COC IF you switch to a larger negative size -- because the larger IC allows you to do this.

[Alan Klein]

Bob, I think the OP's question is the relationship between the image circle and the circle of confusion?

I think I figured it out. The aperture allows the same size of light through it regardless of the image circle size. SO the COC is the same. You only select a different portion of the image circle when you use movements. So the size of the image circle does not matter. The COC will always be the same for the same aperture and focal length, and negative and print size.

[Bernice Loui]

Lens image circle is independent of Depth of Field_Depth of Focus and "circle of confusion"..
~Keep these two lens specifications separate and independent.

~Keep in mind there is only a single point (plane) of true or absolute focus for any lens, any lens aperture.

~What lens aperture does is alter/increase what is percieved to be in focus.. ala "stopping the lens down" increases what is percieved to be in focus.. This does NOT mean what appears to be in focus is actually at the lens point (plane) of focus.

Exampled here using an on-line calucator previously posted by Alan.. Plug in 4x5 image format, lens focal lenght= 200mm, Distance = 30,000 ft, pick any lens aperture. Results will be total DOF= infinity.
https://www.pointsinfocus.com/tools/depth-of-field-and-equivalent-lens-calculator/#{%22c%22:[{%22f%22:19,%22av%22:%221%22,%22fl%22:200,%22d%22:3048000,%22cm%22:%220%22}],%22m%22:0}

Then change the numbers to:
lens focal lenght= 200mm, Distance = 3 ft, lens aperture= f22. Results will be total DOF= 77.7mm.. What happened?
https://www.pointsinfocus.com/tools/depth-of-field-and-equivalent-lens-calculator/#{%22c%22:[{%22f%22:19,%22av%22:%2222%22,%22fl%22:200,%22d%22:914,%22cm%22:%220%22}],%22m%22:0}

The "circle of confusion" or what is percieved to be in focus comes into play or that pesky way to Nature that enforces how lenses must function (the way rays of light are bent by any lens) with zero options for any lens designer/ maker.

What a view camera can offer is the ability to alter/bend the point/area/plane of where the lens is focused. Coupled with this circle of confusion ala what is percieved to be in focus can aid in creating images that deliver the visual perception of what is in focus and what is not in focus.

What is tolerable for circle of confusion or percieved to be in focus is highly depedent on magnificantion/enlargement of the orginal image captured. Greater the magnificantion/enlargement, smaller the circle of confusion or what is percieved to be in focus becomes.. Or, why 8x10 close up images made using an exposure aperture of f90 (even pinhole) can be contact printed and appear GOOD.. if this same image is magnified/enlarged 100X not good at all.


Bernice







Morning everyone and happy Friday!

There are two 210mm lenses available to purchase for my 4x5 camera. One has an image circle of 250mm and the other has 400mm. I'm curious if I would get deeper/ more/ wider depth of field from the larger image circle lens, when I have the exact same shooting parameters, namely:

- f/22
- 2m subject distance

I appreciate your time. Thank you!

[Drew Wiley]

"Circle of confusion" is four self-confused photographers sitting in a cigar smoke-film room debating how sharp an image must be at a "normal viewing distance" they can't agree on either, because they all left their reading glasses home.

Getting more to the point : If you are trying to decide which of two lenses of the same focal length that is best for your own needs, it would be helpful to state what those two choices specifically are, and what camera and film format you have in mind, as well as the subject matter. 400mm is a really huge image circle for a 210 lens if all you have in mind is 4x5 format.