Archived posting to the Leica Users Group, 2001/02/08

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Subject: Re: [Leica] Re: DOF, thanks Austin
From: Johnny Deadman <>
Date: Thu, 08 Feb 2001 17:48:57 -0500

on 2/8/01 2:02 PM, Austin Franklin at wrote:

>> I do not understand why some people cannot accept that the generally
>> accepted definition of coc and depth of field is in fact tied to film
>> size.
> I understand that you have cited some unknown, unsubstantiated, reference
> (of which I am not saying you don't know the source, and can't substantiate
> it) that claims this, but that doesn't make it 'correct'.  It just makes it
> some amorphous method that some manufacturer supposedly uses.
> As has been pointed out, how DOF is 'determined' should be re-thought, and
> possibly standardized, or at least certainly qualified.

Austin, Austin, Austin.

Did YOU bother to look up the definition of DOF before you wrote that?

The Focal Encyclopaedia of Photography is totally clear about it, as is
Ansel Adams (and I might say every other photographic reference I am aware
of). Go through the derivation, which is not at all difficult, standard
Euclidian stuff, and you'll see that it is not remotely amorphous. In fact,
the accepted definition of DOF is remarkably well thought out, even if you
disagree with it. It assumes perfect lens, perfect film and perfect
printing, and is keyed to a standard degree of magnification, which differs
according to format.

It is, moreover, TOTALLY standardized.

In other words it represents a usable MAXIMUM apparent depth of field at a
given degree of magnification. This is very useful and simple. The only
issue I have with it is that the CoC values assume you'll only look at eg
8x10s from 35mm. It's childs play to substitute whatever CoC values you like
according to the magnification you expect.

Your version of DOF may have its uses, but it isn't DOF as generally
understood, which is why you need to call it something else, as I suggested
a while back. Then perhaps people can evaluate it rather than arguing with

Stop digging!

- -- 
Johnny Deadman

Replies: Reply from Rob McElroy <> (Re: [Leica] Re: DOF, thanks Austin)