Eric Pederson
16-Mar-2001, 14:29
Here's two not-quite-newbie-anymore questions:
1) Is there a physically relevant reason that development adjustments for recipr ocity failures are given for some films and not others? For example, Kodak E-31 suggests a -20% dev time for most B/W films at the +2 stop speed (10seconds), bu t no dev time adjustment for TMax films (even over 100 seconds for +2 stops). My understanding (and all I've found in the forum archives) is that contrast is generally increased with prolonged exposure, since clearly the darker areas of t he negative will be receiving proportionally less light and therefore the contra st range should increase as these areas suffer proportionally greater reciprocit y failure. I can't see why this would be different just because a certain amount of reciprocity failure takes longer to come into effect with some films. For th at matter, Ilford doesn't mention dev adjustment for, e.g. FP4+. That could be a matter of company preference, but I don't understand the difference within the same Kodak document.
2) To get more detailed than is probably necessary to just take a picture I'm sa tisfied with: How do I calculate a reciprocity failure dev adjustment on a sheet scheduled for N+ or N- processing?
2a) N+1 with, e.g. Tri-X at 1+ seconds, might be the natural result of the lengt hened exposure, suggesting that if N+1 is desired, I should lengthen the exposur e according to the tables, but not adjust development.
2b) N-2 (etc.) seems trickier. I'll hypothetically start with Tri-X, which I wil l rate at E.I. 320, D-76 1:1 for 10 minutes for N dev. I want to reduce the cont rast to N-2, so I estimate E.I. 160, D-76 for 7 minutes (-30% dev time). I note that this EI gives a meter rating of 10 seconds for the chosen f-stop. I adjust the exposure to 50 seconds according to Kodak's table and rush the negative into the D-76. How long do I develop for? Choice 1: 5.6 minutes (10 - 30% - 20%), i.e. serially additive. Choice 1': 5 minutes, i.e. just add 30%+20% and then subtract (surely this can't be correct!) Choice 2: Some other figure, because the calculations can't be simply added. Choice 3: You are going to get into serious trouble not making lengthy expensive tests for each possible combination of reciprocity failure and desired contrast , so no figure can be given as an equation based on your normal development time .
Needless to say, I would prefer to hear choice 1! I may even act according to ch oice 1 if choices 2/3 aren't going to give dramatically different results, but I remain curious about the "correct" formulation. You can also see why my first q uestion (film types) affects this latter question....
Thanks in advance and sorry for the overly long question -- I couldn't figure ou t a way to ask it more succinctly.
1) Is there a physically relevant reason that development adjustments for recipr ocity failures are given for some films and not others? For example, Kodak E-31 suggests a -20% dev time for most B/W films at the +2 stop speed (10seconds), bu t no dev time adjustment for TMax films (even over 100 seconds for +2 stops). My understanding (and all I've found in the forum archives) is that contrast is generally increased with prolonged exposure, since clearly the darker areas of t he negative will be receiving proportionally less light and therefore the contra st range should increase as these areas suffer proportionally greater reciprocit y failure. I can't see why this would be different just because a certain amount of reciprocity failure takes longer to come into effect with some films. For th at matter, Ilford doesn't mention dev adjustment for, e.g. FP4+. That could be a matter of company preference, but I don't understand the difference within the same Kodak document.
2) To get more detailed than is probably necessary to just take a picture I'm sa tisfied with: How do I calculate a reciprocity failure dev adjustment on a sheet scheduled for N+ or N- processing?
2a) N+1 with, e.g. Tri-X at 1+ seconds, might be the natural result of the lengt hened exposure, suggesting that if N+1 is desired, I should lengthen the exposur e according to the tables, but not adjust development.
2b) N-2 (etc.) seems trickier. I'll hypothetically start with Tri-X, which I wil l rate at E.I. 320, D-76 1:1 for 10 minutes for N dev. I want to reduce the cont rast to N-2, so I estimate E.I. 160, D-76 for 7 minutes (-30% dev time). I note that this EI gives a meter rating of 10 seconds for the chosen f-stop. I adjust the exposure to 50 seconds according to Kodak's table and rush the negative into the D-76. How long do I develop for? Choice 1: 5.6 minutes (10 - 30% - 20%), i.e. serially additive. Choice 1': 5 minutes, i.e. just add 30%+20% and then subtract (surely this can't be correct!) Choice 2: Some other figure, because the calculations can't be simply added. Choice 3: You are going to get into serious trouble not making lengthy expensive tests for each possible combination of reciprocity failure and desired contrast , so no figure can be given as an equation based on your normal development time .
Needless to say, I would prefer to hear choice 1! I may even act according to ch oice 1 if choices 2/3 aren't going to give dramatically different results, but I remain curious about the "correct" formulation. You can also see why my first q uestion (film types) affects this latter question....
Thanks in advance and sorry for the overly long question -- I couldn't figure ou t a way to ask it more succinctly.