Slide film, is normally developed in two steps. By increasing time in the 1st developer you can increase the film speed, though that decreases quality somewhat. Slide film has no latitude to spare if you over or under expose by 1 stop you normally have to pull or push the development. Of course you can get into a thing like I did once where I inadvertently overexposed by 1 stop and the lab pulled it 2 stops ruining it in the opposite direction.
B&W can be custom developed to just about anything. Before Techpan some folks used to develop litho film in super compensating (low contrast) developers to to get extremely fine grain film at a very low speed (5-10). You can go the other way and get very high speeds from ordinary film.
In all these cases there is a quality v speed trade off.
--
Lon Williamson wrote:
I trust William Robb's opinion, and I've heard him write (man, now THAR's a conundrum) many times that C-41 cannot really be pushed. Why is it that such is true of neg film, but not slide film?
-- graywolf http://graywolfphoto.com
"You might as well accept people as they are, you are not going to be able to change them anyway."

