NOTA BENE: I spelled 'coefficient' incorrectly in the title!!!
I am posting this thread in the color section because most who do color also do B&W.
I have found that with C-41 the deviation from standard temp is OK if you adjust for the development time. I get no crossover when I do this. I have settled upon using 1.05 as my factor for development time adjustment. What does this mean?
Say you get great results with 3 minutes at 100 F. If you wish to develop at 90 F you multiply 1.05 by 3, ten times. Put 1.05 into your calculator, then X, then 3, then press = ten times to drill down to the answer for 90 F. You will have a new development time of just under 5 minutes for 90 F. If you drill down to 80 F you will have a development time of about 8 minutes. With some calculators you MUST put in the factor first but, online, the calculator had to be given the current development time first.
Going the opposite direction you must divide the factor into the original time.
It works with C-41 and I have also tried this with traditional Metol/Hydroquinone B&W developers as well. It works there also. I know that, at least theoretically my offering will not hold out for all developers (maybe with D-23, using only metol this might or might not work) but I find this a great help and aid. Please be apprised of the fact that I agitate continuously during development. (This might play a part with contrast consistency because the results with '30 second' intervals at 3 minutes total development time might differ from '30 second' intervals with double the overall development time.) Continuous agitation precludes opening up this discrepancy. Importantly, this coefficient factor also (advantageously) affects needed fix or blix time as well.
Admonishments to the contrary, especially concerning potential crossover with C-41, are theoretically justified I guess, but the negatives and prints still look great and, more importantly, consistent, regardless of the time used. Here, I am trumping pragmatism over the more academic, scientific response. Thus, the inferred caveat. - David Lyga
PE will probably want to kill me for this one.... I had a darkroom that in winter would run about 14C, I would heat everything up to ~3C above what I needed, by the time I was done development, it would be ~3C below what I wanted, C41 got this treatment, no time adjustment. Perfect results, every time.