Tom etc.,
I've used Kodachrome 25, 64 , 200, Velvia , Ektachrome 320 T on OM 2 and OM
4 camera's lots and lots and never implicated film reflectance differences
as an issue. Besides, if it were an issue, why would virtually every other
manufactures have adopted the OTF metering scheme for flash exposure? Also,
remember that the differences in film reflectance become an issue only at
shutter speeds significantly shorter that 1/60 second, since only then is
the light reflecting off the completely open shutter gate, from film held
by the pressure plate, into the silicon photo diode, that is then used for
determination of longer exposure times. Contrast this with the reflection
off the pixilated white paint pattern off the shutter curtain
(approximating an 18% reflectance) at speeds 1/60 and higher . As the
shutter speed gets higher and higher and the gap between the shutter
curtains narrow, and the curtain reflection becomes a greater component of
the overall integrated light signal with less and less from the film
surface. The reflection off the first curtain actually sets the initial
exposure and in the case of a long time exposure, changing light levels
reflecting off on the film surface might affect ultimate exposure duration.
In my own experience, the speed regime where the film reflectance is the
dominant contributor , Film Reciprocity is the dominant variable,
especially with Kodachrome Films.
At 11:41 AM 12/9/99 -0500, Tom Trottier wrote:
>Perhaps the angle of the reflection matters? So that the meter in the
>camera sees less variation?
>
>Tom
>
>On 1 Dec 99, at 15:02, Acer V <olympus@xxxxxxxxxxxxxxx> spoke about "film
reflectance was Re: [OM] OM-2S," saying
>
>> On Wed, 1 Dec 1999, Ian A. Nichols wrote:
>> :
>> :On Tue, 30 Nov 1999, Ken Norton wrote:
>> :
>> :> With various types of film, I too get variations in the 1-1.5 stop area,
>> :> but usually find that the OTF exposure is the more accurate than what
the
>> :> viewfinder shows. (Again, different patterns).
>> :
>> :That's weird - how does the OTF system know what compensation to give
>> :for different reflectance films?
>>
>> Uhm, haven't we been through this one before, with GReese posting
>> reflectance of films here, and the consensus being they're all very close
>> to each other?
>
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Kurt Hurley IDS 2000 Product Marketing Manager
Schlumberger T&T - Diagnostic Systems
1601 Technology Drive San Jose CA 95110
email khurley@xxxxxxxxxxxxxxxxxxx
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