### Calculating Dev Times for new Kodak Films

greenspun.com : LUSENET : B&W Photo - Film & Processing : One Thread

With a view to the future for those of us who extesively use the Kodak films which are about to be changed and will have different developing times, I have the following question for those of you who are photochemistry experts:

After finding a new developing time for, say, Normal Development for a specific film, say Tri-X Professional, is there any formula I can apply to arrive at my other development times that I have already calibrated for the older version of the film, e.g. N-1, N+1, etc.?

More specifically, would applying the same percentage of change to the other developing times get me in the ball park, or is their some kind of proportional relationship that needs to be applied, or is there no specific relationship at all (in which case all the calibrations will have to be done again from scratch!).

Thanks in advance for the expert input.

Regards, ;^D)

I

-- Doremus Scudder (ScudderLandreth@compuserve.com), April 08, 2002

Doremus, I wouldn't over-science this too much. Who's to say what N+1 is? Apply some conversion factor and monitor the results. If you're not satisfied, noodle the numbers a little.

R

-- (ricardospanks1@yahoo.com), April 08, 2002.

A simple multiplication factor should be more than accurate enough. Just divide the new time by the old time to get the factor and then multiply all your N+, N- times by that.
Say the old recommended Kodak time was 6 minutes, and the new one is 7.5; then your factor would be 1.25.
Multiply your own calibrated times by that, and you should be close enough.

There are some published results that seem to show there's a proportional relationship between the induction time (time to first appearance of a visible image), and the development time to a given density of ANY developer with ANY film. Whether that information has any practical use aside from inspection developing is another matter. This 'Watkin's factor' was used quite widely before the time and temperature method became normal practice.

-- Pete Andrews (p.l.andrews@bham.ac.uk), April 08, 2002.