Note... The Zone II is probably 0.40. While the model does try to define Zone I. So 1.45 isn't the aim.
Note... The Zone II is probably 0.40. While the model does try to define Zone I. So 1.45 isn't the aim.
Most of my paper curves incorporate flare. Instead of contacting the step tablet, I usually enlarge the test. I don't want to have to add more quadrants.
From a tone reproduction basis, Jones found, “for the soft papers, the density scales of the negative (DR) should in most cases exceed the sensitometric exposure scale of the paper (LER), whereas, for the hard papers, the density scales of the negatives should in most cases be less than the sensitometric exposure scale of the paper (LER).” I've factored in this concept into my developmental model.
Bill, we both forgot to mention that speeds derived from using the fixed density point of 0.10 over Fb+f are only accurate for "normal" using the ISO standard's contrast parameters.
True, we didn't get into that.
I take comfort knowing the Delta-X criterion explains that speed doesn't change significantly with changes in development time, when you look at how little the 0.3 Gradient point moves with changes in development time.
And so I understand the speed I find with the ISO contrast parameters, might be OK as the benchmark for that film/developer combination - regardless how long I plan to develop it. Though I still mark my graphs with 0.10 speed points, I appreciate that speed point doesn't have to be 0.10
I brought up Delta-X as a question of the practicality of doing a speed test for most people. It's unrealistic to expect valid speed results without a sensitometer and proper methodology. The best that can be expected is comparative results between films or developers. I believe time is better spent first understanding what film speed is and isn't, picking an EI that works with your personal shooting and metering style, and focusing the testing instead on contrast determination. The ISO speed is a valid speed that can be used to base a personal EI. A test that doesn't produce a reliable and verifiable result isn't worth doing.
I am with you 100% that the best tests an individual can do successfully with a minimum of effort... is to determine contrast for development times.
Mario can tell us if the film speed tests were helpful... for the purpose of learning.
One thing I learned here was the value of checking shutters (which I always used at nominal speeds before this exercise).
Amen. I came to the same conclusion having dabbled in practical sensitometry over the last three years. The reasoning, for me, is driven by my experience that adjusting small-area, local ("micro") contrast is much harder under the enlarger, than making larger sweeping changes, made easy with VC filtration, while film latitude in exposure tolerance is phenomenal, nowadays, for the films I used, Delta, HP5+ and Tri-X.
All in all, my main use of the film testing/ZS/sensitometry is for the contrast control of the things I cannot (yet?) easily control under the enlarger, even with VC. In practice, it means that I'd no longer indicate N, N+1 etc on the basis of the overall scene range, which I know I can control by other means (VC) but almost always by the localised needs in complex areas of the scene, which I expect would give me grief while dodging, burning, or masking.
EI is almost a secondary concern to me, as long as it is safe enough to have shadow detail on the film.
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