One more on reciprocity failuregreenspun.com : LUSENET : Large format photography : One Thread
I am not having much luck with the results from various long exposures, not helped by the fact that the information on the Kodak and Ilford data sheets appears pretty vague. Not surprisingly, given the nature of reciprocity failure, I am ending up with far too much contrast in the mid-tones, and muddy shadows. What techniques have others used (i) to determine the additional exposure required to counteract the low illumination of the shadows that causes the film to fail to respond predictably, and (ii) adjust development accordingly? (The main films I use are TMax100, Delta 100, and Tri-X.) It can obviously be done well - vide David Fokos' or John Sexton's work, but it is not working for me at present.
-- fw (email@example.com), July 23, 2000
All the films you mentioned respond differently when exposed for times longer than a second. The reciprocity departure (it doesn't really fail) for T-max is less dramatic than for the other two. When making really long exposures, you have to also contend with altered contrast in as much as portions of the scene typically need less additional exposure causing their respective parts of the negative to gain density faster than others. This needs to be compensated for in development, which of course can make an even longer exposure required to prevent loss of detail in the darkest portions of the scene. The interesting thing about the T-max emulsions is that they seem to withstand longer exposures without encountering this problem. I think 15 minutes is about the limit, if I remember correctly. Some suggested values for TMX are: for 1 sec. expose 1 sec.; for 2, 2.5: for 4, 6; for 8, 11; for 15, 27; for 30, 1'05. For Delta 100, a 1 sec. exposure really needs to be 1.5 sec. and when you get out to 30 seconds, better give 2 minutes. At about 12 seconds with Delta 100, you need to start backing off development to contain build-up of contrast. This is why I use TMX and TMY as I find myself working earlier and later in the day. On my last trip (end of June in western NY state), I made an exposure on TMY rated 240, at about 8:00PM with an adjusted exposure of 1'35" (meter said 30 seconds) and normal development. Got just what I hoped for. I hope this is of some help.
-- Robert A. Zeichner (firstname.lastname@example.org), July 23, 2000.
Try going to the Kodak website at www.kodak.com and click onto the "service and support" web page. From there you can find extensive information on all of Kodak's products. Much more than is available on the data sheets. - Dave
-- Dave Richhart (email@example.com), July 23, 2000.
I believe it was Howard Bond that wrote an article for Photo Techniques on reciprocity effect. It had some really good charts for T-Max films and a more generic chart for other films. I believe that this article was also placed in one of their special issues on black and white. Worth a look.
-- Jeff White (firstname.lastname@example.org), July 23, 2000.
T-grain films are supposed to show less loss of film speed then ordinary silver based films when used for long exposures. Robert has already given some sound advice. But as a rule of thumb when I'm approaching meter readings of 1/2min. I tend to give 3x the exposure so this now becomes 1,1/2min. Problems set in when really long exposures are indicated, I did a couple recently, one at 6min. and one at 8min. and there was no difference in negative density(this was on Polaroid 55 P/N).So it is by no means an exact science. However both negs. printed well on grade 2 paper. When I use Delta100(rated at ISO/80) for long time exposures I do cut back on development by about 20% and process in pyro, this combination allows me to err on the side of caution. So with long exposures overexposure is better then under providing you cut back on development time. I hope this is of some help, regards,
-- Trevor Crone (email@example.com), July 23, 2000.
The Howard Bond article referenced above provides you with some added data on figuring exposure in these circumstances. But you will also need to alter development. Sexton's TMX EI at 40, plus his use of TMax RS 1:15 in the slosher or in a Combi tank--some developing tank where you can control agitation, should provide you with excellent negs. Bob
-- Bob Moulton (firstname.lastname@example.org), July 23, 2000.
Thanks for the helpful replies. For exposures beyond 30 seconds, I was thinking of using something like EI32 - 40 with TMax100, and then using a developer combining two bath development with staining - e.g. DiXactol. In theory, this should enable full development of the shadows while restraining the highlights. Any comments on this?
If someone could get me a copy of the Howard Bond article, I would be very grateful.
BTW, Mr Zeichner - that is a superbly designed web-site, with photographs to match!
-- fw (email@example.com), July 24, 2000.
You could try pre-flashing the film to lift the shadow detail. This is a tricky procedure that requires a lot of experimentation to get it right. What you really need to do is reduce the contrast between the shadows and the rest of the scene.
Here's a suggestion. Wrap a sheet of white paper around the inside of your bellows. This will scatter the highlights and partially fog the shadows. If you're lucky, it'll do much the same thing as pre-flashing. Maybe you won't need to cover all of the bellows, perhaps a few strategic bits of paper will do the trick. I've found that low-tech solutions are always the best. (based on sound theory, of course)
-- Pete Andrews (firstname.lastname@example.org), July 24, 2000.
That really is an excellent idea, Trevor. I have been meaning to try to find some plexiglass to insert into the filter compartment of a Lee compendium for some time for the purpose of pre-exposure, so now I have another reason to get on with it. In fact, the major problems I have had have been with Delta100, when I have been trying to combine a long exposure (say 2 1/2 minutes), with something like an N+2 in pyro - it just hasn't worked. Maybe if I had developed to an N time instead ... oh well. I think that this DiXactol stuff might just do the trick as well - we'll see.
-- fw (email@example.com), July 24, 2000.
fw, pre-exposure can help with shadow detail when adequate exposure is not possible. I personally prefer post-exposure. It is the same idea as pre-exposure but you make the additional exposure after the image exposure, preferably when I am back home and in a more controlled environment. I usually just shine a light at a white wall and focus my camera at infinity, then place the camera 2 or 3 feet from the wall and expose the previously exposed film with an additional exposure of zone I or zone II. No need for any additional equipment or thought ahead of time.
-- Jeff White (firstname.lastname@example.org), July 24, 2000.