In a message dated 99-10-15 13:20:59 EDT, you write:
> Thanks very much for that valuable quote! I seem to recall when I first
> posted my film reflectance measurements that nobody knew an answer to the
> question "What did Olympus base their assumptions on?" Sure looks now
like
> the film industry has killed the assumption that OTF metering mimics 18%
> reflectance.
>
> Gary Reese
Canon had a 1969 patent concerned with reading the light from the film during
exposure to get a proper flash setting. Minolta held the patent that Olympus
used for the OM-2 system, which was a system that combined light readings
from the film plus a reflection off of the front of the shutter curtain
before exposure. Canon's system and patent suggested a switch for
compensation between light and dark film reflectivity. When Minolta made
their own measurements with 44 different film types, they found little
variance between the various films with the lowest percentage reflectance
with Gevapa Dia at 23 percent and the hihgtest with Kodak recording film at
31 percent (both of which were seldom used at the time.) My guess is that
they centered on 26% which was the reflectance of Kodachrome X at that time.
Olympus and Modern Photography did their own studies that confirmed Minolta's
results.
Warren
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