FILM SPEEDS vs DEV TIME

[david_lyga]

<p>We all (should) know that, traditionally, the slower the B&W film, the less development needed to achieve a constant desired gamma (contrast level). Certainly, comparing Pan F+, Plus-X, and Tri-x this fact will bear out. (Slight deversion: In the special case of TMAX there is no official difference (hardly) between dev times for the '100' vs the '400' versions but I believe, after redundant testing for important shadow detail, that the '100' version's official speed is really overstated by a stop and that giving this extra stop exposure would necessitate lessening the dev time (in conforming with the theory) for the '100' in order to 'lower to normal' the increased contrast from the extra density.) But, the case generally stands that the lower the B&W film speed the less dev is needed, OK? Now, my question to you sages is this: Why, with C-41 do we not have this congruent scenario? ALL color neg films, regardless of speed, are processed in the same way! Why? Is not color film really three B&W layers that incorporate dyes to become the lasting image (after the silver image is totally washed away with blix)? Why do fast color films not demand more development? Or, inversely, why do not slower color films demand less development? What am I missing here? Thanks in advance. - David Lyga.</p>

[bobcossar]

<p>It's because C-41 is a saturation process. Only one combination of time/temp/agitation can deliver proper proceessing to all 3 colour layers. Regards, Bob</p>

[randrew1]

<p>Bob is correct that "Only one combination of time/temp/agitation can deliver proper proceessing to all 3 colour layers." Once the process had been established and automatic equipment built to deliver the standard time, it was easier to design new films to fit the process rather than modify the process for each film. I know film builders who would have liked to have a longer development time for 800 speed film, but the process was locked in and changing it was not acceptable. </p>

<p>It is possible to push and pull film (longer and shorter development) to change the contrast. Since all three layers don't change in unison, there are always some compromizes with pushing and pulling. </p>