Quote Originally Posted by Bill Burk View Post
There is no definition correlating density to a particular Zone,
Thanks Bill. When I initially tested/calibrated my film as per WBM I established a relationship between N+/-s, my film speed, film density and zone number (etc).

I actually exposed a Process test roll last night using the steps I outlined above and found zones III to VIII were within half a zone of my target. This is moderately encouraging. I noticed that zone III was a bit high in density, zone VIII a bit low and I calculated the gamma/CI to be 0.4 rather than the target gamma of 0.5 for those conditions.

I have a number of possible explanations for this. The most likely possibility is my XTOL stock (mixed using distilled H2O) is slightly less active than it should be as it is 1 year old and this was the main reason I wanted to do this test to see if it was still "OK". I will either extend my development to compensate or mix up another batch. I hate wasting half of what I mix up !! (I know I need to shoot more films !!)

The other less likely explanation is the formula I used to adjust the development time is not sufficiently accurate (I have never validated it for use). The temp I initially calibrated my film at was 20degC, my Process roll was developed at 23.1degC. I use the formula: Dev time adjustment with temperature.png to determine the new dev time. I obtained the formula from this relatively comprehensive webpage on XTOL.

regards
Peter