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

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Subject: Re: [Leica] how can the 75 Lux focus go bad?
From: Martin Howard <howard.390@osu.edu>
Date: Wed, 07 Feb 2001 15:54:49 -0500

austin@darkroom.com jotted down the following:

> I disagree.  If you take the same lense, and use it on ANY size film, at the
> same distance, you will get the same DOF.  Optics doesn't know what the film
> size is, and adjust it self accordingly.  3' IS 3', no matter what the film
> size is.

This is only true if you don't assume that the lens is supposed to cover the
whole film format.  Most people will make this assumption.  Few people will
put a 35mm f/1.4 ASPH on a 4x5" camera and expect it to cover the film.

> I don't disagree that if you change the distance, to re-frame the image so it
> is the same composition you will get different DOF, but that is not part of
> the discussion...the DOF calculator keeps the same distance, just changes in
> the film format change the resultant DOF it gives you.  I believe that is
> wrong.

Well, basically, you believe wrong... ;)

M.

- -- 
Martin Howard                     | "Why don't they make gravestones
Visiting Scholar, CSEL, OSU       |  cheerier?"
email: howard.390@osu.edu         |                  -- Nigel Tufnel
www: http://mvhoward.i.am/        +---------------------------------------