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Nicola,
The answer is "No". The only way to determine
the reciprocity is to measure it. Kodak does reciprocity testing only up
to several seconds (they offer exposure compensation instructions for long
exposures of seconds duration). When I started doing reciprocity
measurements out to 4-1/2 hours in 2002, Bert Katzung on the APML was in
contact with a Kodak executive about film issues. Bert forwarded some of
my data to his Kodak contact. The reply was interesting in that Kodak had
never seen data on exposures more than seconds long. They saw that we were
serious about film performance, and asked us to survey the market. We
simply didn't (and don't) have enough market potential for Kodak to make
money producing great film for astrophotography.
You can determine reciprocity by measuring the
amount of image loss (photographic "stops") compared to a normal photo (I used 1
second as a reference). A description of the process and the formulas are
in both Michael Covington's book and Robert Reese's book. However
both of these references show examples out to 128 seconds. I found that
reciprocity is not constant for most films over time, and also reciprocity
varies for each color layer in color film (both negative and slide
film).
Don
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