[Leica] B&W film speed

["Gib Robinson" <robinson@sfsu.edu>]

To LUGers with darkrooms:

Recently Nathan Wajsman listed the ISO/EI speeds he uses to expose various
B&W emulsions (Delta 100 at EI=80, etc.). The impression I get from his post
and from other posts on the topic of film speed is that he and others of you
with darkrooms generally shoot a given B&W film at the SAME ISO/EI speed
irrespective of lighting conditions. Is that true? If so, WHY? (As my
daughter so frequently says these days).

Those of us using commercial labs may not have the option of varying
development times, but I assume those of you with darkrooms DO change BOTH
exposure times and development times to control contrast. For example, for
PAN films in high contrasting situations (rodeo riders in bright sun at high
noon), I would be inclined to over expose (effectively increase the film's
ISO) to preserve shadow detail and under develop in the darkroom to control
high lights. That way, I would be likely to get a smoother, more printable
negative to work with.

So, if I have access to a darkroom and I'm in control of the films
development process, I don't just assign one ISO/EI number to an emulsion. I
may have a base number I start from under "normal" lighting conditions, but
I vary that number according to the specific lighting conditions I face when
I shoot a roll and the specific sort of results I want with respect to
contrast range on the negative. Am I making sense here? Is that how you
folks with darkrooms work or do you stick with one film speed for each
emulsion?

- --Gib