In Reichmann's Luminous-Landscape article on Understanding Depth of
Field he starts off defining Circle of Confusion as "A group of
photographers sitting around trying to understand Depth of Field"
<http://www.luminous-landscape.com/tutorials/understanding-series/dof.shtml>
Nowhere is that more apparent than trying to convince some folks that
the concept of Depth of Field begins with enlargement factors and human
visual acuity. Assumptions about visual acuity, print size and the size
of the related Circle of Confusion are all hidden from view by
manufacturers having standardized as far back ago as the 1930's upon
0.033mm as the "accepted" value for 35mm CoC. No doubt, the DOF marks
on your OM lenses are probably based on it as well.
Since your lenses are marked with the DOF by the manufacturer it must be
gospel. Your user's manual never mentions print magnification as being
involved in DOF, therefore it cannot be! I can remember being called a
liar (and worse) by insisting that DOF varies not only by focal length
and aperture but by print magnification as well. Heresy it was!
Anyhow, for some interesting comments on the origins of 0.033mm as the
choice for Circle of Confusion on standard DOF markings and tables see
this article by Erwin Puts:
<http://www.imx.nl/photosite/technical/DoF/DoF.html>
Chuck Norcutt
usher99@xxxxxxx wrote:
> Should have thanked Piers for the very nice references. I don't
> recall the "enlargement factor" being accounted for in the usual DOF
> considerations, though certainly affects overall resolution and
> "quality." I'll defer to Dr. Focus et al. Mike
>
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