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TRI-X development time
I have read a number of posting that rate TRI-X at 280 ISO but I have never
heard how the film is processed. Is there a set of guidelines for processing TRI-X at leaser ISO? Alan Tippett |
#2
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TRI-X development time
"ATIPPETT" wrote in message ... I have read a number of posting that rate TRI-X at 280 ISO but I have never heard how the film is processed. Is there a set of guidelines for processing TRI-X at leaser ISO? Alan Tippett Film is not really adjustable in speed. When the developing time is increased or decreased there is a change in the _effective_ speed, which Kodak calls the Exposure Index, its as good a term as any. Now, changing the amount of development mostly affects the contrast. As time is increased the high exposure areas grow in density faster than the low exposure areas, however, all increase to some degree. The ISO speed is measured at a fixed contrast. Actually, the standard specifies a range of exposure stated as a log ratio to obtain a log ratio of density with the lowest density specified as being logE 0.1 above gross fog and base density. If the film is developed to a lower contrast than the one specified in the standard it requires more exposure to obtain a minimum usable density in the shadow areas. Conversly, if the film receives more development some reduction of exposure is possible because the shadow areas will be somewhat denser than they would be for normal development. Reducing exposure is not absolutely necessary but helps to avoid overly dense highlight densities. The amount of change in development time to effect a given amount of contrast change depends on the film and developer. Conventional films, like Tri-X, will change about one paper grade when development time is increased or decreased about 33% from the "normal" time. The variation depends somewhat on the developer, but is mostly a characteristic of the film. Tabular grain films like T-Max will give the same change in contrast with only about a 25% change in time. The speed difference will be about +/- 3/4 of a stop for this much contrast variation regardless of the film. Now, not all developers deliver the same speed at normal contrast. At one time the ISO standard specified a developer but it was complained that this developer bore little relationship to those used in practice, so the standard was changed to allow the use of any developer, provided it was specified along the the resulting speeds. The variation in speed with developer types is also around +/- 3/4 stop. Some Phenidone developers yield about 3/4 stop greater speed and some developers, notably Rodinal or Microdol-X full strength, loose about 3/4 stop. Both of these vary with dilution. D-76 has become the defacto standard developer for determining speed and the comparisions above are in relation to it. If the Tri-X you mean is the ISO-400 variety (roll and 35mm film) EI-280 is about 70% of the rated speed so one of the speed loosing developers will give you this speed with normal contrast. Now something about exposure. The ISO standard yields about the very minimum speed that will give good shadow detail. Actually, many photographers find that increasing the exposure, which is the same as shooting the film at a slower speed, gives better shadow detail. Because the film is tested for the minimum exposure for good tonal rendition there is lots of latitude on the increased exposure side and almost none on the reduced exposure side. I've gone into this detail because I think its not very well understood. In fact, if you want to use Tri-X at EI-280 you can develop normally in any developer but the negatives will be a bit dense if you use a speed increasing developer like Microphen or Xtol, and will be pretty normal if you use D-76, HC-110 or Rodinal. A clue to the amount of latitude is that the pre 1960 ASA standard had a 2.5 X safety factor built into it. The current ISO standard has a 1.25X factor, so the old speeds were just half of the same film now. At the time the ASA speeds were generally considered to produce excessively dense negatives and it was common practice to use less exposure. Now we have a standard with minimum exposure and a lot of people increase it. To make the point, shoot some tests at bracketed exposures about 1/2 stop over a range of about 2 stops more and less than the film rating. Develop normally and see what you get. That will give you a very good idea of what sort of tonal rendition you will get for a given exposure index. -- --- Richard Knoppow Los Angeles, CA, USA |
#3
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TRI-X development time
In general and within a limited range increasing exposure affects mostly
shadow detail, more exposure with Tri-X yields better shadow detail. Processing times should not be altered from your normal time unless you also need to adjust overall scene contrast. In my experience Tri-X is very forgiving or overexposure errors and I usually expose it at EI200 and may expose at EI100 for scenes with short contrast ranges. If you have a long exposure range you can push your highlights up onto the shoulder area of Tri-X's exposure curve and reduce highlight contrast. Useful for those black and white shots of black tuxedos and white wedding gowns. As an experiment I'd suggest shooting frames at EI 800, 400, 200, 100 and 50 on both a roll of Tri-X and a roll of TMax 400 and process both rolls in the same small tank at you standard time for either film (should be fairly close developing times anyway) and then make the best print you can from each of 10 negatives. Then subject the prints to a blind comparison from ten knowledgeable photo buddies and ten tyros. Have each of them rank the 10 from best to worst. -- darkroommike ---------- "ATIPPETT" wrote in message ... I have read a number of posting that rate TRI-X at 280 ISO but I have never heard how the film is processed. Is there a set of guidelines for processing TRI-X at leaser ISO? Alan Tippett |
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