Film Testinggreenspun.com : LUSENET : Large format photography : One Thread
I recently established a film speed of 320 for Tri-x. I have been attempting normal 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 recommendations 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 got net densities of .7 and 1.08 and at 6 minutes .75 and 1.13. The Zone V part seemed ok, but I seem to be in zone VII rather than VIII at the upper end. I assumed upping the develpment time was not an option because zone V would then be too 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 zones on one sheet. I used different shutter speeds for the different exposure sessions. Any ideas before I start again ?
-- Paul Mongillo (firstname.lastname@example.org), May 04, 1999
When testing for effective film speed, vary your exposures by changing the aperture 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 error into the determination of your effective film speed.
Also, in your procedure, are you taking the base + fog value into account when you establish Zone I? At the risk of being redundant, remember that the proper determination 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 density. The highlights, of course, are determined by development time. Since the determination of effective film speed is the first step, an error here could have an effect of subsequent calibration procedures.
Admittedly, sensitometry can at times be frustrating, but the end result is quite rewarding because everything is keyed to your individual method -- your own camera, shutter, exposure meter, developing, printing and seeing. Good luck!
-- Matt Long (email@example.com), May 05, 1999.
Thanks Matt. Actually I did use a constant shutter speed for testing. What I meant was that I changed the shutter speed for the second set of normal film developing tests I did. I varied the aperture for achieving the desired zones in each case. I wanted to see if a different shutter speed would act differently. Also 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 tri-x is wrong. I'll try again. Thanks.
-- Paul Mongillo (firstname.lastname@example.org), May 05, 1999.
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.
-- Alan Gibson (Alan.Gibson@technologist.com), May 06, 1999.