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View Full Version : XPan and depth of field

Mike Lopez
05-29-2009, 09:22 AM
A lens of a given focal length will provide more depth of field at a given aperture when used for a larger format of film than it will for a smaller one. I.e., a 45mm lens at f11 can display more depth of field on a 6x7 camera than it will on a 35mm camera, if properly focused.

My question is how this could be applied to the use of an XPan. The depth of field scale on the 45mm lens for this camera seems appropriate for the 35mm format. But when using the camera in the panoramic format, won't there be more apparent depth of field? Say I focus at the hyperfocal distance and take a picture with the camera set for the 35mm, then switch to panoramic and take the same picture. Won't the nearest point of the depth of field move closer to the camera? Can this be accounted for in any way in real use of the camera?

Or am I entirely missing something here?

bdial
05-29-2009, 09:36 AM
Depth of field for a given focal length doesn't change with film format. It may be less apparent in a larger negative, but the circle of confusion is the same.

Steve Smith
05-29-2009, 10:02 AM
I would consider it equal or very similar to a format which shares the dimension of the longest side.

e.g. a 6x6 or 6x7 format will be similar to the 24 x 65 format.

The depth of field with the Xpan will be the same When exposing a 24 x 36 frame or the 24 x 65 frame. It will only change if you enlarge the 35mm frame more than the wide frame.

Steve.

TheFlyingCamera
05-29-2009, 10:31 AM
Depth of field does not change with post-exposure enlargement.

David A. Goldfarb
05-29-2009, 10:49 AM
Depth of field as a calculated value most certainly does depend on the film format and is not unrelated to enlargement factor. The size of the actual circle of confusion may be the same on film, the the size of the acceptable circle of confusion, which is necessary to stipulate for the purpose of calculating a DOF table or scale, is usually given relative to format (making certain assumptions about the resolving power of the human eye, normal print sizes and viewing distances), though for any given purpose requiring greater or less enlargement, one might decide to use a larger or smaller value for acceptable CoC, or without going to the trouble of calculating it, you might decide to look at the DOF scale and stop down one or two stops from the recommended f:stop, if you think the recommendation doesn't give you a sharp enough image for your taste or your planned print size.

Colin Corneau
05-29-2009, 01:30 PM
Interesting, since you can switch mid-roll from 24x36 to 24x65...the depth of field can't change from shot-to-shot.

Sirius Glass
05-29-2009, 01:59 PM
Why should it?

The optics are the same before and after switching.

The distance from the optics to the film plane is the same before and after switching.

All that changed is the length of the film that is exposed which is perpendicular to the optical axis.

Steve

Q.G.
05-29-2009, 02:25 PM
"Depth of field [...] not unrelated to enlargement factor."

So unless you print both panoramic and normal frames to the same height (i.e. same final magnification), DOF will be the same.
If you however decide that both size frames are to be printed equally wide (i.e. not the same final magnification), DOF will indeed be different.

David A. Goldfarb
05-29-2009, 02:28 PM
The DOF can certainly change from shot to shot if the format changes. I can change format easily on a large format camera while keeping everything else the same, and the DOF changes by definition when the format changes, because DOF is defined in relation to the print (making certain assumptions about typical print sizes, etc., as described above), not the image on film. If the format is larger, then the acceptable circle of confusion--the diameter of a blur circle that can be resolved as a sharp point on a typical print at a typical viewing distance by a typical human eye--is larger, and DOF values cannot be calculated without plugging in a value for acceptable circle of confusion.

Steve Smith
05-31-2009, 09:47 AM
It will only change if you enlarge the 35mm frame more than the wide frame.

David is right, my wording is wrong.

Depth of field is defined by acceptable sharpness and by circle of confusion.

Enlarging a frame of 24x65 to a width of 12" may look accepatable. If you then enlarge a frame of 24x36 to a width of 12", which is almost twice as much enlargement, the sharpness may no longer be acceptable.

Steve.

tiberiustibz
05-31-2009, 10:07 AM
It's all based on enlargement factor. It will appear different based on how much you enlarge the negative. It is different, but enlarging only the center portion of the negative would give the exact same results as 35mm.

jbbooks
06-01-2009, 02:26 AM
"Depth of field [...] not unrelated to enlargement factor."

So unless(sic) you print both panoramic and normal frames to the same height (i.e. same final magnification), DOF will be the same.
If you however decide that both size frames are to be printed equally wide (i.e. not the same final magnification), DOF will indeed be different.

With the XPan, the above would be correct, but I think the word "unless" should be "if".

The point is, with the XPan, it is implicit that the amount of enlargement is the same with only the aspect ratio changing from one view to the other. We might argue about what Hasselblad determined to be the "acceptable" enlargement of a 35mm film camera image, but whatever was eventually agreed on would not change just because the film gate was wider. Images made on my XPan are no different than those on my Contax as to how much they can be enlarged before I consider than to be unacceptable, never mind which mode was used--so long as they are enlarged the same amount, which is to say, to the same height.

Q.G.
06-01-2009, 05:54 AM
With the XPan, the above would be correct, but I think the word "unless" should be "if".

Quite right. My mistake.

The one thing with DOF is - as you do too say - that the final magnification of the image is what counts.
The other thing is that it depends on what someone thinks to be still acceptable or already unacceptable.
The third thing that it is a comparative thing too: DOF is much larger in an image in which the 'true' sharpness is nothing to write home about than it is in an image in which the 'true' sharpness is incredibly detailed.

So the final thing about DOF is that we should not be bothered with the thing beyond a very basic level. (Which is: Put focus where it needs to be, and then use the aperture to control how the other bits look. No use in trying to quantify the thing. No use in format comparisons. All that counts is how your image turns out.)

dwdmguy
06-22-2009, 06:25 AM
Super interesting question. Here I am just working with my old xpan, and I get a pretty neat result. Take a look at this picture, not mods', and it looks as if it was shot via a T/S lens....