This is both film specific and general question. What happens to the contrast of the negative if I increase the concentration of the developer? Decrease the concentration? (but adjust the time accordingly to get adequate density) What would happen if I changed from D76 to an Agfa developer? Would it be better or give me some special effect?
As long as you adjust development time accordingly, contrast should not be affected by concentration or dilution of D-76. Kodak says that D-76 at 1:1 increases accutance. I have also noticed a smoother tonal gradiation with D-76 1:1 vs D-76 stock. A more dilute developer may seem to lower contrast due to compensation (will require reducing the agitation also), or developer exhaustion. I'm sure Agfa would recommend using their developers with their films. I don't think that you can make a blanket statement that it would be better to do so. You'll have to try it out, and see how it works for you.
