All of this is my own experience; YMMV and I won't feel bad if you don't like it, agree, etc...
I started using Diafine when I lived in Peru and had no access to electricity, regular running water, etc. It was a reliable developer to use in the field at relatively high temperatures (water temps at or above 80 F)... and I have basically used it as my standard developer since then. I have mostly just used it as directed on the packaging with the following modifications:
- I use a 4 min pre-soak in water with 4 drops of Photo-flo before I start development - - I know, the box says no pre-soak, but I didn't burst into flames when I tried it, and it solved the problem of very stubborn airbells on some films - - remember, YMMV
- I use 4 min in each solution rather than 3 min and I invert the tank 2-3 times gently every minute - - I get streaky processing if I do not invert.
Until recently, I did this the same for all film sizes (35mm, 120, 4x5, and X-ray). However, based on Sandy King's excellent work as published in View Camera, I have modified my process for 4x5 film and have gotten excellent, entirely reproducible results and it has become my new standard and I am testing it now for 120, as well:
- 4 min pre-soak as above, with Photo-flo
- 4 min in each solution (A & B) that has been diluted 50% with water
- Continuous agitation in all steps on a Uniroller base that reverses direction every 1.5 rotations
- Rinse with water & fix normally
I think that Sandy would see the influence of his testing here...
Perhaps because 90% of my shooting is here in TX and I think we have exceptionally high natural contrast, the above process has worked very well to help tame the contrast. I take at least 3 meter readings for most 4x5 shots and still worry when the maximum spread is too high, but the above process has really helped deal with it. On negatives from less contrasty days, I do have to print with higher contrast filters (often #4) where I would have otherwise liked a 2.5 or 3, but that is a small price to pay to be able to put all my film in the same Jobo tank and process it all together (Heresy!)
I have also begun cross-processing C-41 color film in Diafine with the above method... the jury is still out. I have several pages of negatives to both scan and print in the darkroom. I am also experimenting with further reduction in the concentration of Solution A (perhaps incorrectly) to see if I can reduce the grain in smaller neatives on some films (specifically Arista) when processed with continuous agitation... I'd like to be able to put a tall Nikor tank of 120 or 35mm reels on the roller base to process, rather than manually inverting, and not get the large grain that appears when I do that size film in Diafine with continuous agitation.