As I am becoming more facile with the zone system, I have realized that I need s ome 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 contracti on. I would choose N-1. Through experience I have now found out that when I cont ract, 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 ? 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 an d the Kodak curve gives an adjusted time of 37.5 seconds due to reciprocity fail ure. 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 counter act this increase in contrast is to adjust development by -20% if I have a meter ed 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 c orrect development? Or do I look at what change in % my N-1 time is from my N ti me, and then add the 20% figure for reciprocity failure contrast increase, and u se this new % to change my N time. Each method will give somewhat different answ ers.
Any other pointers would be welcome!