At 16:12 10/16/00 , Dan Lau wrote:
>I am wondering if there is any difference in the amount
>of light reflected in exposed film vs. un-exposed film.
>For example, when testing one of the OTF models (OM2 to
>OM4(T(i))), does it matter what type of film is put in
>the film chamber during the test. In my thinking, there
>are (at least) the following possibilities:
> Un-exposed film [a fresh roll every time, expensive]
> Exposed (but un-processed) film [if I use the same
> roll of film to test several bodies, this is what
> I'll end up with]
> Processed un-exposed film [this is just clear film]
> Processed exposed film [in this case, does it matter
> what is on the film?]
>
>So does it matter which type of film I use to check out
>the OTF meter accuracy of an unknown body? Thanks.
I would use un-processed film. Doesn't matter much whether it has been
exposed or not. Yes there is a slight color change. I would *not* use
processed film.
Processing removes the anti-halation layer allowing light to reflect off of
the pressure plate, and the reflectance from processed film could be nearly
anything depending on whether it was exposed, exposed for photographs,
simply pulled out of the cassetted and exposed to light, etc.
I've not found much variation in TTL OTF metering between films, but then I
haven't used all that many different types either; at most maybe ten or so.
-- John
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