Adjusting the Exposure Index or EI (ISO is a labratory tested rating of the film in a specific developer) adjusts where the shadows fall on the film curve. Using a lower number EI generally indicates using less development to "fit" the larger scene contrast range onto whatever output media you happen to use, and vice versa.
Originally Posted by /dev/null
You ought to get a fair feel for this after about 10 or 20 rolls at each EI.
Mark Barendt, Ignacio, CO
"We do not see things the way they are. We see things the way we are." Anaïs Nin
Start and do it by the book. Learn the rules first, then you can eventually break them by experimenting on other developers. I started with D-76 and Kodafix (all kodak products) for neutral results.
on a web forum you're going to get suggestions from conservative to off the walls as to what you should do
shoot a roll in similar lighting conditions and develop.
bracket your exposures by 1 fstop each way ( over - normal - under )
after you process your film, look at your negatives, notice which of the exposures "worked " for you ...
then use that information for your next roll ..
good luck !
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I hate to disagree with the others here, but I would start out shooting it at 50 and developing about 15% less than the manufacturer recommends. I usually find that this gives better shadows, and easily printable (and scanable) negatives. I would then adjust from there.
If you can, I would try to workout the exposure and development for good wet printing, even if you are scanning. This way you have the option of either. I find my scanner can yield good results with a range of negatives. Wet printing is harder if important shadow details fall on the toe of the film curve (as will most likely happen at box speed). With a scan you can fix this somewhat with a curves adjustment, but why not get it right to start with.
The kind of overexposing and underdeveloping films shot under normal (not contrasty) light is common among large format photographers, but doesn't work well with 120 and 35mm films. Tmax 100 in D-76 1+1 for Kodak's recommended time at EI-100 is perfect for 120. Rodinal does lose a stop of speed with this film, so I shoot it at 50 for Rodinal developing.
Originally Posted by L Gebhardt
Tmax 100, 645 format, EI-100, D-76 1+1
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Unlike many other black and white films, TMX 100 generally works best at the rated speed of 100.
Over or under exposure can cause problems. So try this speed first until you get the dev times right.
You want to be most concerned about the placement of deep shadows and those max highlights in
which you wish to be able to print some detail. I have no experience with Rodinal. My preferred dev
is PMK, but I have done TMX in 76, Perceptol, TMRS, HC-110 too. Most developers work well.
Originally Posted by DREW WILEY
What developing time are you using for PMK and Tmax 100? I love PMK for Tri-X but haven't had a chance to try to work out a developing time for Tmax 100.
Interestingly and backing Drew Wiley's point is that Ilford do not even quote a time for TMax 100 or 400with Perceptol at less than box speed.
Pentaxuser - in my opinion that is a faulty bit of documentation in Ilford's Perceptol instructions (indeed I find their recommendations for non-Ilford films somewhat simplified). I use a lot of TMX with Perceptol at various dilutions and if you want to maintain Perceptol's ultra-fine grain effects, TMX should be downrated (as should any film) if you want good shadow separations. With most general purpose developers box speed is quite usable for TMX (although I still prefer a little more shadow contrast so I rate it a little slower), but Perceptol is different. If you develop to box speed you lose Perceptol's characteristic qualities.
Let me preface the following remarks by stating I have never used Perceptol with TMax but we seem to be building a picture on APUG that Perceptol always needs a one stop reduction or even more for any film.
This may be the case but it just seems significant that for D100 Ilford gives a time at EI 50 but not for TMax 100.
So did Ilford make a mistake with TMax 100 and 400 or simply not bother to try it at lower than box speed?
Seems poor marketing to curtail tests on other makers' films. For the sake of a short saving on testing time Ilford gives the impression that no reduction in box speed is necessary and yet if it clearly is, the user then decides that Ilford can't be trusted on other makers' films so users move away from Perceptol and Ilford loses users.
It just doesn't sound like the kind of Ilford that the vast majority of APUG puts its trust in