Re: [Leica] DOF

[Martin Howard <howard.390@osu.edu>]

Robert Appleby jotted down the following:

> Maybe there are really two concepts here, film-plane DOF and print DOF? The
> latter can be varied by enlarging the negative more or less, but the former
> is determined solely by subject distance, focal length and aperture.

What you call film-plane DOF is not soley determined by subject distance,
focal length, and aperture.  It is also determined (and this is *critical*)
by the size of the CoCs that you are willing to accept.  I believe that in
35mm photography, a standard circle-of-confusion size is 0.03mm.  If you
plug a different CoC size into the equations, the DOF will change even
leaving the subject distance, focal length, and aperture the same.

Once you stop thinking of DOF as an objective property and start thinking of
it as "the zone of perceived sharpness around the focus plane", you realize
that DOF "around" the subject, on the negative, and in the print are all
just different ways of looking at the same thing.  It is just a convenient,
standardized representation of the limits of visual perception as it
pertains to photography, and not conceptually different entities.  Outside
the equations, in the "real" world, DOF doesn't exist.

M.

- -- 
Martin Howard              | There's a culture here which dictates that
Visiting Scholar, CSEL, OSU| anyone who walks more than a few paces must
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www: http://mvhoward.i.am/ | insane, or British.    -- David Willis, BBCWS
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