Figuring out developing times

[henryjjames]

Hello all,

I am seeking advice on how to calculate development times when the film/chemistry manufacturers do not provide the data, nor is it available on the massive dev chart. Does anyone have suggestions or methods on how to calculate a development time for a film other than pure trial and error?

Thanks,
Henry

[tim.bowman]

Lots of folks like the Massive Dev Chart for this. But I actually prefer trial and error. Take your best guess, make a print, and see how it goes. If you're struggling with shadows, give the film more exposure next time. If it's too contrasty, develop less. If it's too flat, develop for longer.

[tundratim]

I built a temperature controlled darkroom timer some years ago and faced this problem. You'll find a spreadsheet on the git repo that calculates these factors a number of different ways:

https://gitbucket.tundraware.com/tundra/devtimer

I used a couple of theoretical mathematical models as well as actual published data from Kodak (and maybe Ilford, I don't recall), and then compared how much they varied from each other.

The actual program has two lookup tables - One for film and one for paper - with correction factors for temps in one degree F increments away from a nominal 68F. These correction factors were the results of the analysis above.