Archived posting to the Leica Users Group, 2001/02/07

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Subject: [Leica] Re: DOF
From: Jim Brick <>
Date: Wed, 07 Feb 2001 16:00:51 -0800
References: <200102070811958.SM00756@m2w073>

At 03:06 PM 2/7/01 -0700, wrote:
>For those of us who think that film format doesn't matter - here's another 
>DOF calculator.

So where does one enter the film format?

One doesn't because it does NOT matter.

Film format does not matter. Focal length, aperture, and image size are the
DOF determining factors.

Many folks use a roll film back on their LF cameras. Let's say you have an
8x10 camera. You take a photograph on 8x10 Tri-X film. Now you slip in a
6x7 roll film holder and take another photograph on 120 Tri-X film. Nothing
has moved. Same camera. Same lens. Nothing tweaked.

Guess what!

The DOF of both the 8x10 and the 6x7 images are exactly the same. Same
image size. Same lens. Same aperture. But the 8x10 obviously has more
coverage. But the same image size. Hence the same DOF.

Same is true if you use a 6x6 back, then the rare 35mm back on a
Hasselblad, or Rolleikin (sp) on a Rollei. Or the Mamiya 7-II with 120/35mm.

Film format has absolutely NOTHING to do with DOF.



ps... for fun, on that DOF calculator, enter 75mm, f/1.4, 2 feet, and see
what the DOF is...  :-)
      then enter 100 l/mm, and recalculate.  :-)

Replies: Reply from Rob McElroy <> (Re: [Leica] Re: DOF -Optical vs Apparent)
In reply to: Message from "" <> (RE: Re: [Leica] how can the 75 Lux focus go bad?)