Tom etc.,
I've used Kodachrome 25, 64 , 200, Velvia , Ektachrome 320 T , and Scala 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 camera manufacture 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 longer 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 of 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, in the speed regime where the film reflectance is the
dominant contributor (long exposure times), Film Reciprocity is actually 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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