I’ve just reread my copy of Kodak Z-121A C41 manual, which as far as I understand it is the original C41 manual; dated 1975. Whatever, it was the first one available that I know of in Australia.
No mention is made of actual capacities like the current electronic manual you refer to, so essentially one would have to guestimate.
I started doing C41 in my Jobo around 30 years ago, at the same time at work we were running a Dip ‘N’ Dunk C41 machine with monitoring using Kodak control strips.
Pretty much the only way you can be certain is to run control strips then either check them yourself, or take them to a lab and get them to check them.
Using a 1520 tank with a 1530 module bolted on, one can run up to 4 x 120 films and a single 35mm film, or in my case a 35mm control strip. I remember trying various combinations with a control strip inserted and eventually came up with various strategies. This is using 600ml of solution, not 1 litre.
For 135 the maximum that could be done and keeping the control strip within the parameters, was 8 rolls of 135 x 36 frames per 1 litre.
With 120 film between 3 rolls and 4 rolls were usually within the parameters; although if my memory is correct, it was just within the parameters with 4 rolls.
Eventually I settled on using a 1540 tank, 1510 + 1530 module, minimum solution is 470ml, I always used 500ml of solution. With this and using C41 120 film, I developed 2 x 120 rolls per 500ml of go juice. Did that on and off for about 20 years, worked a treat. That of course doesn’t mean it was on the money from a technical point of view, but it was pretty good and the colour prints I obtained were at times devastatingly good.
You need to understand that Kodak invented the process, they were the best ever technical company to deal with and if they suggest that so many rolls of film per litre is the go; then you can bet that suggestion is correct for perfect developing.
One can always deviate and still get wonderful development, day in day out, many do and I did. Just remember to carefully observe your results with what you develop and choose which parameters are acceptable to you.
As a matter of interest, all of the control strips that I did in my Jobo, were super consistent when compared to the control strips that went through our Dip ‘N’ Dunk C41 machine. This is a normal state as the replenishment system can sometimes be thrown off kilter with sporadic film numbers going through, followed by heavy throughput, then nothing for an hour or so then off again with a shed load of 8x10” and 4x5” interspersed with maybe 30-40 rolls of 120 going through when a job lot came in for processing.
Disclaimer: I haven’t done C41 for close to three years now, although I may in the near future as I recently picked up some 4x5” C41 film; 40 sheets of Ektar 100.
Mick.