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I recently established a film speed of 320 for Tri-x. I have been attempting no rmal development tests. According to Ansel you should expose several sheets of film at zone V and zone VIII. Continue upping your develpment from manufactures recommendations until zone V has a net density of .60 to .75 and zone VIII has a net density of 1.15 to 1.35. I realize I have incorporated the density recomm endations for both diffusion and condenser enlargers. Unfortunately things seem to have gone a little haywire for me. At five miutes in T-max RS at 68 F in go t net densities of .7 and 1.08 and at 6 minutes .75 and 1.13. The Zone V part s eemed ok, but I seem to be in zone VII rather than VIII at the upper end. I ass umed upping the develpment time was not an option because zone V would then be t oo high.I thought perhaps I had exposed things wrong so I did a couple over and zone VIII was even lower. I used a dark slide cut in half so I could get both z ones on one sheet. I used different shutter speeds for the different exposure se ssions. Any ideas before I start again ?
When testing for effective film speed, vary your exposures by changing the apert ure rather than the shutter speed. Try to use 1/125 or 1/60 for the majority of your test exposures -- these speeds tend to be more accurate in leaf shutters. Variences in the accuracy of different shutter speeds can introduce a slight er ror into the determination of your effective film speed.
Also, in your procedure, are you taking the base + fog value into account when y ou establish Zone I? At the risk of being redundant, remember that the proper d etermination of your effective film speed is essential for proper shadow detail. The Zone I value should be approximately 0.1 above your film's base + fog dens ity. The highlights, of course, are determined by development time. Since the determination of effective film speed is the first step, an error here could hav e an effect of subsequent calibration procedures.
Admittedly, sensitometry can at times be frustrating, but the end result is quit e rewarding because everything is keyed to your individual method -- your own ca mera, shutter, exposure meter, developing, printing and seeing. Good luck!
Thanks Matt. Actually I did use a constant shutter speed for testing. What I m eant was that I changed the shutter speed for the second set of normal film deve loping tests I did. I varied the aperture for achieving the desired zones in ea ch case. I wanted to see if a different shutter speed would act differently. Al so the densities I presented are minus film base plus fog. I was more succesful for my normal develpment test for T-max last night. Maybe my film speed for tr i-x is wrong. I'll try again. Thanks.
I've just drawn a couple of quick graphs of zones vs density, assuming that in both cases Zone I density is 0.1. The Ansel curve has slightly higher contrast at the top end. Paul's has slightly lower contrast at the top. Neither is a straight-line from Zones I to VIII.
The conclusion I draw is that the film/developer combination that Paul is using has different characteristics to Ansel's, which is not really suprising. The shape of the curve is different, and no amount of changing EI or contrast will make the curves coincide. Paul: if you want to replicate Ansel's results, you should probably use the same developer as him. Even then you might have difficulty; Tri-X has probably changed since his day.
Whether is is worth trying to replicate Ansel is a question that only Paul can answer. I find Ansel's suggestions are rather low-contrast for me, and I don't care at all that my curves are a different shape.
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