BTZS Film Testing Question

[jeroldharter]

I am getting ready to test two films in two different developers, so 4 tests.

If I were using BTZS tubes, or tray processing, or slosher processing, this would not take much time. But I use Jobo Expert drums which are great for cranking out film but tedious for testing.

So I want to mix the two films, e.g. Both TMY2 and HP5 in the same drum so that I can reduce the number of processing runs by 50%.

Any known problems with that? I will be using Xtol 1:1 and D23.

[Oren Grad]

If the films deplete the developer at different rates, theoretically you could end up with results different from what you'd get with only one film type. But I have no idea whether the size of such an effect would be large enough to worry about. What solution volume are you using, relative to the nominal capacity of the developers?

[jeroldharter]

The standard volume in a Jobo 3010 tank is 500 ml for up to 10 sheets, although I would have just two sheets in each drum. So there should be no depletion of the developer.

[Oren Grad]

Well, running two sheets in each drum during your tests if you normally run ten, but using the same overall volume of developer, is potentially an even bigger concern in this respect. IIRC John Sexton includes a fogged sheet or sheets if necessary to fill out an Expert drum load, to make sure that developer depletion rates are at least roughly similar across all sheets and runs. But AFAIK he hasn't shown sensitometric data to justify that level of concern.

[jeroldharter]

I do have some fogged sheets to add. However, I think that a sub threshold surface area of exposed film relative to the volume of stock developer solution would be a negligible variable. But, that is why I am asking, because I am not certain. I will add a sheet or two of fogged film to each run.

[ic-racer]

The Jobo 2820 test-tank holds just two 4x5 negatives. I use that for testing. The 2830 holds two 8x10 sheets.

[Bill Burk]

I work for Kodak but the opinions and positions I take are not necessarily those of EKC (I work in a graphic arts digital business unit, D2L).

I did some tray processing tests last month using some old D-76 and I only used 1 ounce of stock solution per sheet of 4x5. I drew a family of curves at 6, 8, 10, 13 and 16 minutes and a Time/CI chart to go with it.

This month I did some live processing with sensitometry. I aimed for CI 0.6 and missed it by 13%.

Where did I go wrong? When you tray process, and pull sheets out at different times, the last sheets in the tray get more agitation

I bet you will not be causing 13% errors no matter how badly your films cross-contaminate or your developer depletion rate.

But I hope my example shows the importance of controlling variables.

I make up for it by plotting new points on my Time/CI chart. So in the end, I still hit my CI.

[Brian Ellis]

Well, running two sheets in each drum during your tests if you normally run ten, but using the same overall volume of developer, is potentially an even bigger concern in this respect. IIRC John Sexton includes a fogged sheet or sheets if necessary to fill out an Expert drum load, to make sure that developer depletion rates are at least roughly similar across all sheets and runs. But AFAIK he hasn't shown sensitometric data to justify that level of concern.

That's my recollection as well from attending one of John's workshops. I don't remember whether he had any sensitometric data to back it up but knowing John, he had something more than a guess that it might be necessary.

[Bill Burk]

IIRC John Sexton includes a fogged sheet or sheets if necessary to fill out an Expert drum load, to make sure that developer depletion rates are at least roughly similar across all sheets and runs.

That's my recollection as well.

Well, I know John Sexton recommends fresh D-76.

If I had used it fresh, and used 2 ounces per sheet, I could have - with no additional effort! - eliminated two of the three suspect variables in my 13%problem.