How to adjust development times when increasing number of film rolls in tank?

[aldevo]

I have a 1L developing tank. I have always processed 2 rolls at a time in the tank using 500 ml of working solution. Odd, yes, that I've *always* processed 2 rolls in the tank with the same amount of working solution but that's the way it's worked out.

I'm curious as to how to adjust the development time when processing 3 rolls with 750ml of working solution instead of 2 rolls with 500 ml of working solution. Let's assume that in both cases I'm using the same film, same developer, same dilution, temperature, etc. In other words the only difference between the two cases is the # of film rolls and volume of working solution.

I'm inclined to belieive that the times would increase slightly, because there would be less fluid flow during tank inversions - but I'd like to hear from folks who actually have observed the differences.

This is just the sort of information I'd hoped would be in the "The Film Developer's Cookbook" but, sadly, it's lacking.

 

[bdial]

For the situation you describe, the time doesn't change.

 

[David A. Goldfarb]

Normally the time wouldn't change in that situation. If you wanted to be really precise, I suppose you could test it with standardized rolls with uniform exposure patches on every frame and measure the difference with a densitometer, but the process is flexible enough to give you plenty of room to compensate along the way for such slight differences. How tight are the tolerances in the rest of your process--shutter calibration, meter calibration, testing of film batches, film storage, developing temperature, agitation method, etc.? I think you would have to do a lot of testing of this sort to notice a difference between two rolls in a tank and three rolls in a tank.

 

[chriscrawfordphoto]

Kodak's PDF on D-76 says you can only do two rolls in a 4 roll tank if you dilute it 1+1, and that you need to increase developing time 10% for each extra roll added. Most developers are strong enough to do 4 rolls with no added time.

 

[ic-racer]

Trial and error.

Your system will probably not have much change. In a Jobo 1500, a single reel, vs 8 reels can have a difference because of slight disproportionate tank to film area proportions and disproportionate fill-empty times with the lift.