Jobo E6 2,5l Kit Capacity

So I have been having this ongoing question for year between my colleagues. How much 16mm 30,5m length film can be developed in this kit?
The box states that "All the processing chemical is concentrated solution to make max of 2.5L working solution which allows processing up to 40 rolls of film (135-36exp or 120 films)".
Calculating by area I would be able to develop 4 rolls of film of 16mm 30,5 length. Which I have done fine for a long time. Recently one colleague did 9 films in the same kit with good results.
There is controversy that Kodak states that one roll of 35mm is a Super8 cartridge (15m), when you calculate by area it is more like 2 rolls of Super8 that makes a 35 mm film.

So what are Your thoughts on this?
Have I been throwing away unexhausted chemistry or my friend did a miracle and developed double than normal amount?

The final question is, how many rolls of 16mm 30,5m length films I can develop in Jobo E6 2,5L kit?

Thanks!

Your numbers look right to me. For the sake of showing one's work, one 30.5-meter roll of 16mm film has a surface area of:



If we employ the standard practice of treating a "roll" of film as having a surface area of 80 in2 (which is approximately correct for 135-36 film), one 30.5-meter roll of 16mm film has the equivalent surface area of 9.5 rolls (i.e., 756.4 in2 ÷ 80 in2 = 9.5). Using the capacity that Jobo states for the 2.5-liter kit (40 rolls), that works out to 4.2 rolls of 16mm x 30.5m film, which is exactly what you calculated.

Jobo's stated capacity of 40 rolls for the 2.5-liter kit is based on reuse of the working solutions. Specifically, they advise mixing the working chemistry one liter at a time and using those same one-liter solutions to develop a maximum of 16 rolls, where the development times for the first developer, color developer, and bleach are gradually increased for subsequent rolls to compensate for the gradual loss of chemical activity. (Similarly, you could mix 500 mL at a time and develop a maximum of 8 rolls, etc.)

Your colleague getting twice the capacity out of the same kit (assuming they're developing the same type/size of film as you) could come down to a couple things. First, they may be making additional extensions to the development times of the FD, CD, and bleach solutions in attempt to maintain controlled development even after going beyond the stated capacity. Second (and probably more likely) is that their films -- specifically the ones developed later in the life of the chemistry -- are not actually attaining correct color density. Chemistry that is past its stated capacity can still produce film that might appear, to the unaided eye, to be properly developed, but checking the chemistry with a control strip and a Status-A densitometer would likely show errors. Of course, none of this matters if the user is okay with how their film looks.

(A slightly wonky addendum to this is that the "useful" part of the film is, as a ratio of overall film width, slightly different between 16mm and 135 formats, such that their respective utilizations of chemistry per unit area is slightly different. But the difference is only a few percent, so that couldn't, by itself, explain what's going on in your colleague's case.)

For my part, I think you've got the more reliable approach. If cost is a mitigating factor, experimenting on some potentially sacrificial rolls is always an option.

Scott J. said:

Your colleague getting twice the capacity out of the same kit (assuming they're developing the same type/size of film as you) could come down to a couple things. First, they may be making additional extensions to the development times of the FD, CD, and bleach solutions in attempt to maintain controlled development even after going beyond the stated capacity. Second (and probably more likely) is that their films -- specifically the ones developed later in the life of the chemistry -- are not actually attaining correct color density. Chemistry that is past its stated capacity can still produce film that might appear, to the unaided eye, to be properly developed, but checking the chemistry with a control strip and a Status-A densitometer would likely show errors. Of course, none of this matters if the user is okay with how their film looks.

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Bingo!

So i can give more details how i work and maybe you can advice more.
The problem i encounter with this is that I do workshops where students shoot a roll of 16mm for thesis practice. And I develop them in Lomo tank, the smaller one, where 16mm is threaded in two stories, 15m each. The tank capacity is 1,6 l to cover both levels of film. Usually i mix the 2,5 liters of jobo e6 and develop four rolls consecutively, meaning that after every film i pour back the "used" chemistry back to the bottle with "fresh" chemistry, somehow replenishing the solution. I do extend times after each roll as mentioned in the jobo manual. After the four rolls there is some significant contamination in the bottles like pre baths and conditioners that as mentioned in the manual is not necessary to wash in between.
My colleague obtained the results using 1 liter solutions and developing half of the 16mm roll in each turn. so he exhausts the one liter for 4 rolls and then mixed another liter to make other 4 rolls, it is viable but counterproductive timewise.
What would be your approach when you have to develop 8 rolls of 16mm 30,5 m in this kit. Would you use 2 kits of 2,5l and to the full rolls in every developing? or would do the colleagues approach and to more slowly by using 1 liter until it is exhausted and then another 1 liter to complete the 8 roll development?

Justas said:

meaning that after every film i pour back the "used" chemistry back to the bottle with "fresh" chemistry, somehow replenishing the solution.

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I know what you mean, but the term 'replenishment' is an unfortunate choice. It's not what you're doing, evidently.

Justas said:

What would be your approach when you have to develop 8 rolls of 16mm 30,5 m in this kit. Would you use 2 kits of 2,5l and to the full rolls in every developing? or would do the colleagues approach and to more slowly by using 1 liter until it is exhausted and then another 1 liter to complete the 8 roll development?

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In the end, in cases like these it's a matter of how you want to spread out the inherent drift in the process. You can work with smaller batches of chemistry and have those drift out of spec quite rapidly, or one larger batch of chemistry that drifts out of spec more slowly. The net result is about the same in terms of how much film you'll have developed in spec by the end of the whole thing. There's not really an inherently best choice out of these two.

So at the end we can come to the conclusion that this kit is suitable to develop 4 rolls of 16mm? with reasonable decency?

I didn't say that, nor do I think this can be deduced from anything I've said.

nono, i dont say that, I just try to find opinions on the subject. How much film you would feel safe to develop in this kit?

I'm sorry, I couldn't say. I'd suggest sticking to what the manufacturer suggests.

koraks said:

I'm sorry, I couldn't say. I'd suggest sticking to what the manufacturer suggests.

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Thanks for Your opinion!
I wrote to Jobo last day and if they respond i will let you know

This could get a little hairy, but here's how I'd approach your problem...

In the chart below, Jobo states that up to 4 rolls of 135-36 can be developed in 1 liter of working solution without the need for extending times in the FD, CD, and bleach. You reported that your tank requires 1.6 liters of working solution to adequately cover the film. That volume works out to a maximum developing capacity of 6.4 rolls of 135-36 without needing time extension (i.e., 4 rolls/liter * 1.6 liters = 6.4 rolls).



Now, if you recall from post #2, we determined that a single 30.5-meter roll of 16mm film has the equivalent surface area of 9.5 rolls of 135-36. If we divide 9.5 rolls by 6.4 rolls, that gives us a dimensionless factor of 1.48. I'm going to call that the "column factor". The column factor tells us which of the four columns (1, 2, 3, or 4) a specific developing scenario corresponds with. Column 1 corresponds with the 1-4 rolls case, Column 2 corresponds to the 5-8 rolls case, etc. A column factor of 1.48 is bigger than 1 but smaller than 2, so that places us in the second column. Ergo, developing a single roll of 30.5-meter 16mm film in 1.6 liters of fresh solution will, in theory, require the times listed for 5-8 rolls.

In general, the formula for calculating a column factor for 30.5m x 16mm film is given by:



Where:

C = column factor
2.375 = unit conversion factor (basically, this arises from 9.5 rolls ÷ 4 rolls/liter)
Nr = roll number (ie., 1 for the first roll developed in that batch of working solution, 2 for the second roll, etc.)
V = volume of working solution, in liters.

So for example, if you then attempted to reuse that same 1.6 liters of working solution to develop a second roll of 16mm film, you would calculate a column factor of 2.97 (i.e., 2.375 * 2 ÷ 1.6 = 2.97), which puts you just barely inside the third column, such that you would need to use the times listed for 9-12 rolls. Of course, that's cutting it a little close, because a column factor of 2.97 is very nearly big enough to move you into the fourth column, in which case you might opt to use the times listed for 13-16 rolls, instead.

Personally, I think the easiest approach would be to mix the entire 2.5 liters up at the same time (provided you have storage containers large enough to do so). The reason for this is because we've calculated that the entire 2.5-liter kit has the capacity to develop 4.2 rolls of 16mm film (at least, that's according to Jobo's capacity guidelines). That number -- 4.2 -- corresponds almost perfectly to the four columns provided in the directions. So, by pouring the used solutions back into their respective bottles after each development session, each successive roll will simply correspond to the corresponding column in the instructions -- i.e., roll 1 uses the development times in the first column, roll 2 uses the times in the second column, etc., etc.

(And just for fun, you can prove this to yourself by using the equation above to calculate the various column factors for a volume of 2.5 liters.)