Critique This Time to Dilution Calculation Technique

[craigclu]

I was recently trying different dilutions of Xtol and was led to some 1+2 calculating. On Usenet, a Francis Miniter posted a simple formula that he uses and after playing with it a bit, it certainly seems a reasonable tool for getting a good starting time. He divides the total parts of dilution 1 (i.e., 1+1 = 2 parts) by the total parts of dilution 2, then uses the square root of that number and adds to the original time. I put it on a simple spreadsheet and played with all manner of dilution relationships and everything calculated to solid feeling conclusions.

I'm attaching a screen shot of the calculation and also a copy of the spreadsheet. Perhaps this has been discussed a bit but I don't recall seeing this simple formula before. Seem reasonable?

 

[Juri]

It would be nice to develop a roll of film in 1 ml of Foma R09 (1:400 dilution) just by increasing the developing time to 33 minutes, but I'm afraid it's not going to happen. There are probably limits to using it, especially with Rodinal.

 

[Ian Grant]

It's a bit flawed Craig. You need to be calculating from the FS, 1+1 and 1+3 times which are rather variable depending on the film emulsion.

I just tried the spread sheet and it gave a 1+3 time that was way under same for 1+2.

Ian

 

[craigclu]

It would be nice to develop a roll of film in 1 ml of Foma R09 (1:400 dilution) just by increasing the developing time to 33 minutes, but I'm afraid it's not going to happen. There are probably limits to using it, especially with Rodinal.

After I posted, it dawned on me to play with more extreme dilutions (my normal go-to developer is PyroCat MC at 1:100, usually falling somewhere at about 1/2 box speed). You're right Jüri, it doesn't work with the extreme concentrations. It did seem to give what seemed to be good starting points on Xtol, D-76 sorts of soups, though. I'm a late-comer to Xtol (I like the "game" of home-brew and resisted) and had started doing some tuning as a full emulsion speed solution and the 1:2 look was working well on a couple of initial trials. I found little reference to the dilution and happened into Francis' post about that time and for the project at hand, it seemed pretty reasonable.

 

[Murray Kelly]

A possible solution (!) might be to work on the numbers and get somewhat reasonable results with the high dilutions and the less diluted will follow but won't be as outrageous as you might expect?