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Re: Correction: film reflectance was Re: [OM] OM-2S and reciprocity fai

Subject: Re: Correction: film reflectance was Re: [OM] OM-2S and reciprocity failure
From: appleb@xxxxxxxxxx
Date: Thu, 9 Dec 1999 17:00:38 -0500
Polachrome films ("instant" transparency films made by Polaroid) cannot be
used with OTF metering because of the extremely high reflectivity of the
film.  The film instructions provide this warning.


end

Regards

Bruce Appelbaum

"Once the rockets are up, who cares where they come down?
That's not my department," says Wernher von Braun.


Kurt Hurley <khurley@xxxxxxxxxxxxxxxxxxx>@zuiko.sls.bc.ca on 12/09/99
01:50:35 PM

Please respond to olympus@xxxxxxxxxxxxxxx

Sent by:  owner-olympus@xxxxxxxxxxxxxxx


To:   olympus@xxxxxxxxxxxxxxx, Acer V <siddim01@xxxxxxxxxxxxxxx>,
      olympus@xxxxxxxxxxxxxxx
cc:
Subject:  Correction: film reflectance was Re: [OM] OM-2S and reciprocity
      failure



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
PH 408-437-5156  FAX 408-437-9031 PG 408-699-4587




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