Re: speed of paper versus film

----- Original Message -----
From: <lwilkinson@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
Received on Thu May 9 16:44:06 2002