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 17:53:45 -0500

on 2/8/01 12:31 PM, Austin Franklin at wrote:

>> No, with respect, you're not addressing my point, Austin. DOF
>> as commonly
>> used (eg in published DOF tables, lens engravings and
>> published formulae)
>> refers to DOF of an image at a particular nominal
>> magnification and has for
>> fifty years. Your definition doesn't.
> I believe DOF (ie, engraved on a lense) is referenced to the film, not to
> any magnification.

The CoC for a given film format, which is a fundamental part of the DOF
equation, is derived from the expected degree of magnification, which is
(IIRC) 8x for 35mm. It's a simple matter to work up a DOF calculator based
on the standard equaltions which derives the CoC value from a degree of
magnification you specify. A glance at the derivation would tell you this.
- -- 
Johnny Deadman