- Original Message -
From: lwilkin...@schilli.com
I'm struggling to understand the relationship between film and photographic
paper. Specifically, calculating exposures, etc.
Where film may be considered ASA 100, paper may be considered P100.
Obviously, it's not the same 100...but what's the relationship?
Papers have 2 ISO parameters associated with them, ISO R and ISO P. The former
has to do with the density range a paper or combination paper+filter is capable
of. The latter is the speed of the paper. Ilford MGIV, for instance, has a
speed of ISO P500 when unfiltered. As for the relationship, take the 500 divide
it by 100 and you will get a rough estimate of the paper's speed when used as
FILM. Using that relationship we find that MGIV has a film speed of ISO-5.
If you do a search of this list messages, you'll find that ISO-6 is a very
common used value, ISO-5 or 6, close enough, IMO. If you use, let's say, a #0
filter, the ISO P speed becomes ISO P200, so your paper will behave,
approximately, as film ISO-2 (I'd approximate that to ISO-3, BTW).
Once you know the film speed of your paper and if you know the f/stop of your
pinhole camera, calculating exposure is business as usual, with the exception of
reciprocity, for which here is a table in a little article I wrote some time
ago:
http://members.rogers.com/penate/pinsize.htm
Hope it helps,
Guillermo
