Quote Originally Posted by Photo Engineer View Post
Mark;
This seems to be a case of the two films being within an hair of each other in D76, but wildly different in your developer. I've seen that and have mentioned my 13 developer experiment where several coatings gave me different results in 12 of the developers but were identical in the release developer.
This means that your work is not done. If different releases of the same product look alike in a standard developer, but look very different in your developer there may be something wrong with your developer. One way to confirm this is to use another accepted developer such as HC110 to see what happens. If these two films are the same, then the fault lies within the developer and not the coating in the sense of this severe variability.
That does not mean that these coatings are good IMHO. The curves still sag too much in the middle. PE
I know I've had problems with non-uniform illumination. Here's an example:

D76Test1.jpg

That big inflection is my fault. I'm learning that it's difficult to photograph a back-lit step-wedge through a lens. A uniform light-source usually isn't uniform enough, and lenses introduce variation in brightness from centre (spelled correctly ) to corner, especially wide open. Here are results after supposedly fixing the problem:

t.jpg

My developer (D316) and XTOL are close, and not wildly different, so I think D316 is fine. The curves are much better, but that inflection is still there in both. Rather than blame Kodak, I'm going to assume this is entirely my fault and (1) add more diffusion to the light-source and (2) use a longer lens. I like Michael R's method of simply taking a bunch of shots at various f-stops of a known light-source.

@Michael R: Flare is another problem that your method avoids. I've recently started taking two shots of the step-wedge, the 2nd with the upper row of wedges blocked to eliminate their blast of light that adds flare to the bottom row. You are correct: That flare pushes up the toe-area. The only reason I'm still trying to get step-wedges to work is so that when experimenting with developer formulas, I can develop two-frame-long strips instead of a roll at a time. I'm interested in seeing your results, and TIA for doing those measurements.

Mark