View Full Version : Extending C-41 Dev Capacity

4-Mar-2017, 08:32
A slightly different slant on this question. Let's assume my kit (Unicolor) is good for minimum 12 rolls before I would need to start monitoring/increasing dev times to account for exhaustion. If I only developed 12 rolls, I'd do them all at 3:15 and they'd look great.

I've seen some formulas like t=140/(40-n) where n=roll number. This makes sense if you're increasing time starting at roll 1, but if you start increasing at roll 13, it's a HUGE jump. At 13th roll, this formula would ask for a dev time of 5:11.

Would you recommending increasing dev time with each roll, or adjust the formula above for a more modest increase starting at 13?


Gary Beasley
4-Mar-2017, 19:04
Probably the best way to use this formula is calculate the number of roll starting your count as roll 12 as number 1.

Mark Sampson
5-Mar-2017, 10:00
I've run a great deal of C-41, but all in large-scale replenished systems. I'd be wary of using your chemistry beyond the design parameters. I don't think stretching your chemistry will be cost-effective. Figuring out your answer will mean trial and error; that means expensive film used, and possibly pictures lost. It will take more time to do this work as well; how much is your time worth? How much money will you save by re-using developer? If doing your own photo process engineering appeals to you, than go ahead. If making pictures is more important, process by the book.

5-Mar-2017, 13:35
I guess I'm lucky. I shoot mostly 4x5 and use tubes. For four sheets of 4x5 film -- the same total amount of film as one 36 exposure roll of 35mm film -- I only need to use 1.5 ounces of C-41. And my tubes rotate in a temperature-controlled water bath. After development, I just dispose of the C-41. That means I can get the equivalent of 21 36 exposure rolls of film (84 4x5 sheets) from each quart of chemical -- and each sheet gets fresh C-41. No need to ever compensate!

8-Mar-2017, 05:34
xkaes what type of tubes and tempering bath are you using? BTZS, Jobo or something else? Thanks.

8-Mar-2017, 08:28
xkaes what type of tubes and tempering bath are you using? BTZS, Jobo or something else? Thanks.

I use Colourtronic gear. It is very similar to the Jobo stuff, but it is no longer available. It was simpler and cheaper than JOBO yet has small to large tubs and tubes -- up to 60" long! I doubt that you will find much about it on the web. GREAT stuff.

11-Mar-2017, 07:57
Thanks everyone. As always great feedback. It's more of a science experiment than true cost savings. Like, rather than dumping chemistry... What would I need to get 3 or 4 more sheets developed if I needed on the same kit.

My question is probably more... Should I increase dev times with each batch (reuse) or only after I've exhausted the book limit.

I know the answer... "well, what does experience tell you?". So, I'll keep focusing on what's most important, actually making the exposures. :)

Gary Beasley
11-Mar-2017, 20:41
I've seen and used recommendations for extending developer life with slide kits by the manufacturer and the gist of it is you extend the times after the stated number of rolls, and the time extension is significant and only good for a few more rolls of film. Personally if you can use a one shot routine, do it.