Depth of Field question

[Harley Goldman]

I was reviewing the depth of field tables on the Schneider website and it led to a question. Assume I am using two lens with my 4x5, a 150mm and a 240mm. I compose a picture with each lens to basically achieve the same framing and perspective, meaning I move back with the 240mm until I have essentially the same framing for both shots.

From reading the tables, it would appear that the 150mm would yield a larger depth of field for the shot than would the 240mm. If that is correct and I wanted to maximize DOF (ignoring movements for the moment), I would always move in and use a shorter lens, all other things being equal. I realize the longer lens should compress the scene, etc. but I am chiefly concerned with DOF.

Am I interpreting this correctly?

[Dan Fromm]

Its funny you should ask.

Please see http://www.largeformatphotography.info/lfforum/topic/499846.html and do the arithmetic for yourself.

Cheers,

Dan

[Harley Goldman]

Thanks for the reference, Dan, but there a few too many formulas for my tastes. Looking at the article made my head hurt no time.

[QT Luong]

For a more intuitive presentation illustrated with images, follow the
link given by Jeff Conrad to Paul's site in that thread (also
listed on lfpi non-commercial resources).

[Jeff Conrad]

If you look at equation (16) in my article, you see that it doesn't contain
the lens focal length. Provided the subject distance is substantially less
than the hyperfocal distance, all lenses used at the same magnification and
f-number give approximately the same DoF.

You can't maintain the same framing and perspective with two different
lenses; the framing is determined by the magnification, and the perspective
is determined by the lens-to-subject distance. Paul van Walree's page
illustrates all of these concepts quite well.