Crossover in film development rather. I've been told that one should not process C41 spec films at the C22 temperature/time specifications because within 5 degrees of 100 you get "crossover"; when one layer is not fully developed while the others are. Can't this be compensated for in an enlarger or (shock) in scanning?
No, it cannot be compensated for in an enlarger, and it is very difficult to compensate for digitally.
When you get a properly processed film, the negative or transparency for that matter, produces 3 layers in which the dyes have identical contrasts and parallel curves. For an illustration see the product characteristic curves on the Kodak web site or Fuji web site.
If a film is incorrectly processed, the three curves are not of identical contrast and are not parallel. If laid one on top of another, they cross, and you get crossover. Therefore, if you have say a red object which is not illuminated evenly (goes from light to dark), it might be orange at one side, red in the middle and green at the other side. Trying to correct for the orange to make it red, moves the green to the middle and introduces a gray or blue to the greenish part. It can make a face look pretty awful as one example.
Even photoshop is rather hardpressed to fix this type of problem and that is why I for one, suggest not getting into that type of situation.
PE
