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From: jer@peora.UUCP (J. Eric Roskos)
Newsgroups: net.rec.photo
Subject: Re: Is OM-4 Junk?
Message-ID: <1415@peora.UUCP>
Date: Fri, 2-Aug-85 09:34:12 EDT
Article-I.D.: peora.1415
Posted: Fri Aug  2 09:34:12 1985
Date-Received: Sun, 4-Aug-85 10:19:48 EDT
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Organization: Perkin-Elmer SDC, Orlando, Fl.
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> If you use Ilford XP1, you can use Zone System doctrine to a limited degree
> by changing the ASA rating for each shot.  Exposed at ASA 100, the neg will
> have much lower contrast than it will when exposed at ASA 400.

Isn't this just an effect of nonlinearities in the "toe" region of the film's
characteristic curve?  I.e., if you underexpose the film and develop it
normally, most of the exposure will end up down in the region where the
slope of the curve is less; which is, of course, exactly the definition of
low contrast (please, no flames on the definition of "contrast index," I
know the CI includes the nonlinear regions.).

A disadvantage of this method, though, would be exactly that the curve
IS nonlinear; so differences between two lower levels of luminance would
be less pronounced than between two higher levels.  This would tend to
produce a loss of detail in the shadows.
-- 
Shyy-Anzr:  J. Eric Roskos
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