On Thu, Nov 13, 2008 at 9:26 PM, William Robb <[EMAIL PROTECTED]> wrote:

> Actually, it depends purely on the magnification ratio and alowable COC.
> Focal length doesn't matter, nor does subject distance.

Your statement is only an approximation, useful for close subject
distances.  See:

http://en.wikipedia.org/wiki/Depth_of_field#Close-up

"Stated otherwise, for the same subject magnification, all focal
lengths give approximately the same DOF. This statement is true only
when the subject distance is small in comparison with the hyperfocal
distance, however."

> Don't try to correct John on this, he's forgotten more than most people know
> on the subject.

I'm not "most people", and he's wrong.   John disputes that the
allowable CoC, which you mention above, varies with format.  I have
provided numerous sources that state otherwise, and offer clear
explanations.

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