Zone System Exposure Questiongreenspun.com : LUSENET : Large format photography : One Thread
As I am becoming more facile with the zone system, I have realized that I need some help with a particular situation as follows:
Let's say that I have a scene with shaddows on III and highlights on IX. I would like to have the highlights on a maximum of VIII so I would like some contraction. I would choose N-1. Through experience I have now found out that when I contract, I need to add a little bit of exposure so that III does not sink down into murkiness. so for N-1 I would probably add ½ stop.
My question is about when I do this AND I have failure of reciprocity because I am shooting in dim light and using long exposure times. I shoot 4x5 Tri-X at EI 160. The particular exposure I have had trouble with was metered at 8 seconds and the Kodak curve gives an adjusted time of 37.5 seconds due to reciprocity failure. Now I understand that the contrast will therefore increase. I don't want it to because I have already made my contraction calculations as above and want my top zone to be VIII. Kodak's only information on development changes to counteract this increase in contrast is to adjust development by -20% if I have a metered exposure of 10 sec. (I am close to this with a metered time of 8 sec.)
Soooo, here is the question:
Do I use my known N-1 time and then take an additional 20% off this to get the correct development? Or do I look at what change in % my N-1 time is from my N time, and then add the 20% figure for reciprocity failure contrast increase, and use this new % to change my N time. Each method will give somewhat different answers.
Any other pointers would be welcome!
-- Scott Jones (firstname.lastname@example.org), February 23, 2002
Your first option is correct. You should adjust the development time for longer exposures based on reciprocity failure last. Therefore, your 20% decrease should be calculated from the N-1 development time you arrived at when first metering (N-1 time multiplied by 0.8). You would probably be OK with the second method too, since the result is not so different. Be aware that the Kodak figures are also just approximations. The goal is a prinable negative, not to get within a few hundreths of the density measurements.
When you add time according to your reciprocity tables for long exposures, you disproportionally expose the film: The highlights react much more to the additional light than the shadows and are, in essence, overexposed. Hence, the reduction in development time. Don't worry about getting into the vicious circle of adjusting EI for the adjusted development time. This isn't rocket science, and the compensation should be built in to the table. The usual disclaimer applies: Your results may vary, so make changes to the tables based on your experience.
Black and white films are very different in their reaction to long exposure times. Since you are using Tri-X and the Kodak tables (which I have found to be quite accurate), you should be well in the ballpark. Note that T-Max films and many Ilford films require no development compensation for longer exposures according to the manufacturers. I can vouch for the correctness of this with T-Max 100.
To further refine and simplify the Kodak system, which can get a bit fiddley with percentages, I use the following as a rule of thumb:
For Tri-X (and many other conventional films) and long exposures, contrast increases approximately 10% for each doubling of the indicated time. For example, if the indicated time is 15 sec., the exposure time, adjusted for reciprocity and extrapolated from the tables, is 80 sec. This is approx. 2.5 doublings (15 x 2 = 30; 1 doubling. 30 x 2 = 60; 2 doublings. 60 x 2 = 120; 3 doublings. 80 seconds is close enough to halfway to say we have a resulting contrast increase of about 25%, equal to roughly a bit less than N+1 development (my N=1 is about 30% more than my N). If you do not want this effective increase, subtract 1 development number (i.e. N-1 minus 1 = N-2) I take this into consideration when determining development schemes, being careful to err on the side of more contrast and more exposure (10 seconds more exposure added to a 100 second exposure is only 10% more!). The 5% less developing time in the above example is inconsequential, so I would give an N-2 development in this case. This is easy to figure in your head, and you can simply round to the closest developing time (N-1 or N-2 etc.) that you already have, thus eliminating pesky "in between" times (N-1- 10% and so on).
The Kodak tables only give adjustments for metered times up to 100 seconds. If you find yourself in situations where you need longer exposures, you can extapolate the continuation of the tables, either by guess or by graphing. I have found, by plotting the Kodak data on a graph, that the scale is basically logarithmic. Using any old computer graphing program (I used the one in Word for Windows), you can extend the curve to give you a table with increased times. Mine goes up to 5 hours (which I have used, exactly once). FYI, my extended times are:
Metered exposure Adjusted Exposure 2 minutes 22 minutes 4 minutes 50 minutes 8 minutes 120 minutes 16 minutes 300 minutes
I usually guess at in between values, again, erring on the side of overexposure.
Interestingly, it is also possible and sometimes extremely useful to expand contrast by using long exposure times. I think the look of prints from negatives expanded this way is different from those from expansion by increasing development, and, one eliminates the increased grain associated with increased development.
Hope this helps. Good luck with those long exposures. ;^D)
-- Doremus Scudder (ScudderLandreth@compuserve.com), February 23, 2002.
Has anybody ever taken 2 exposures, then cut the first negative (before development) up into say...4 one inch stips. One could then develop each of the four stips at 4 different process times, and determine which of the four times gives the wanted density. Now one can safely develop the other exposure with confidence. Does this make sense to anyone but me? As I haven't tried this myself, maybe I'm fooling myself that I could cut a negative in the dark? Or is there some other problem that I've not figured yet...or...maybe this is common, and I'm not that original... :)
It's no different than the way we "test" paper with increasing exposure times across the paper.
-- Douglas Gould (email@example.com), February 23, 2002.
Doremus' response was excellent, so good in fact it should be in a book somewhere.
I can add two things: One, get Fuji Acros film for your long exposure work. It requires no exposure or development compensation for up to 120 seconds (thereby making it more sensitive than Tri-X once you pass the 10 second exposure meter reading), and only 1/2 stop compensation ad infinitum. And there is no compensation required for reciprocity contrast increase. These are Fuji's claims for this film, but they have been born out in my work and I can say this film is remarkable for long exposure work.
When you need compensation beyond N-1, I strongly recommend diluting your developer and reducing agitation over simply reducing development times with full strength developer. You will achieve much better highlight control and better midrange separation, with minimal, if any, loss of film speed.
-- Ted Kaufman (firstname.lastname@example.org), February 23, 2002.
Scott: Doremus' advice is sound in my experience with TRI-X. I've started using HP5+ for long exposures and I used the Kodak TRI-X adjustments, cut development 20% and got great results. I'd also stress again how hard it is to screw this up and how approximate the numbers are in real life. If you meter past dusk and look at your table and come up with a 3 or 8 or 10 minute real time exposure, don't forget that the light is getting dimmer and dimmer and dimmer while the exposure is going on. You would be amazed how much light you can lose in an open field in 10 minutes some early evening. The end of the exposure can be in light that is 2 EV #'s or more less than where you started. (Or gain if you're an early bird) The negative is probably going to be fine though.
-- Kevin Crisp (KRCrisp@aol.com), February 23, 2002.
Just develop by inspection and you won't have to be bothered by all those numbers. And after a short time you'll never miss one.
-- Michael A. Smith (email@example.com), February 23, 2002.
Scott - A similar question came up a while ago. Someone was getting flat negs when exposing for extended times with the development adusted as per the manufacturer's recomendation. I'll not repeat everything here (you can search it in the archives) but here's my short answer: In many cases you actually shouldn't compensate for extended exposure with reduced development. This is because most really long exposures are made in light which doesn't have as large a brightness range as "normal" (i.e. daylight) exposures. Try it - just shoot (compensating for reciprocity, of course) and develop as normal. You may find you prefer it this way. I know I do.
Another point concerning reciprocity (w/ trad films)on really long exposures (in the multi-minute range): It's hard to over-do it, so don't be shy about leaving that shutter open! (Plus, as someone mentioned, it's getting progressively darker as the minutes wear on.)
-- Mark Parsons (firstname.lastname@example.org), February 24, 2002.
I love lower light shooting. I think the increased local contrast due to the longer exposures often translates into a much more lively print. Here's what I do (HP5 @ 200, FP4 @ 50): Meter shadow, calculate the reciprocity exposure adjustment (from your chart), and cut this exposure in half for a ZONE IV. Often a ZONE III will not hold detail in instances of greater compensation (esp. if you opt for shorter development times versus higher dilutions or reduced agitation) Then meter the highlights to determine required compensation. In moderately low light, when highlights meter for times of less than a second, just choose a development to allow highlights to fall in a ZONE VII or VIII. I vary development time about 20% to move a highlight a zone's distance. When highlights meter for times longer than a second, I apply reciprocity exposure adjustment to the highlight value as well before using it to calculate development. When both highlights and shadow are on the "same side" of the reciprocity line, everything works in your favor (very cool), requiring less compensation than when they are "split".
I think the suggestion was also made to have have at least two exposure of the same shot, so that a second negative can be processed with necessary adjustments based on your first try. After a while, you get so good that this just becomes a back-up negative. I usually do a little dance when this happens.
-- Chris Jordan (Boston) www.jordanphoto.com (email@example.com), February 25, 2002.