Diafine Developer Question

Hi Everyone,
I've been reading through 'Way Beyond Monochrome, 2e' and found in the chapter 'Customizing Film Speed and Development' some basic suggestions on establishing effective film speed and development times to compensate for different subject brightness ranges. The 'quick and easy' approach recommends using:
box speed for low contrast (e.g rainy or foggy day)
cutting film speed by 2/3 stop and developing time by 15% for normal contrast (e.g bright but cloudy day)
cutting film speed by 1 1/3 stop and developing time by 30% in high contrast settings (e.g bright sunny day).
This sound pretty straightforward when developing with, say, HC-110 but how would this work with diafine which suggests uprating your film? I have both developers.
The authors also give an example of downrating ISO which also includes a drop in developer temperature (ISO 400/27° becomes ISO 250/25°) so it seems like there's a third variable; developer temperature. Am I reading this correctly? Temperature isn't explicitly mentioned in the paragraph describing this approach so I, a complete darkroom neophyte, would welcome some clarification.
Many Thanks
Adam
As an aside, Diafine developing has been touted as having the advantage of handling multiple ISO ratings on the same roll of film (I've read the same claim with rodinal stand development) and I'd be interested in hearing anyone's experience in this regard.

imyself said:

Diafine developing has been touted as having the advantage of handling multiple ISO ratings on the same roll of film (I've read the same claim with rodinal stand development) and I'd be interested in hearing anyone's experience in this regard.

Click to expand...

A film has only one ISO rating and that is determined by the manufacturer. What you are referring to is what is know as the Exposure Index or EI. "This refers to a speed rating assigned to a particular film and shooting situation in variance to the film's actual speed. It is used to compensate for equipment calibration inaccuracies or process variables, or to achieve certain effects. The exposure index may simply be called the speed setting, as compared to the speed rating." If what you proposed were true then a manufacturer would only have to make one speed of film and the user could determine for himself what ISO he wanted. Obviously a false claim. When you under expose film (use a higher EI than the ISO rating) you lose shadow detail. There is no way of escaping this. No developer or developing method can bring back what is not there. The shadow information was never recorded on the film. This seems to be the hardest thing for those new to photography whether it be analog or digital to understand.

When you use a two bath developer like Diafine you sacrifice flexibility for convenience. The film speed and contrast are essentially locked in by the developer. This is different from conventional developers where contrast can be varied by changing development times.

In 'Way Beyond Monochrome, the chapter 'Customizing Film Speed and Development' is a simplified explanation of what is know as the Zone System. Whole books have been written on this subject not just a single chapter. To fully understand what is going on you need to read one of these books. However with the availability of variable contrast paper there is less need for varying the contrast of negatives.

Diafine is split developer, the first bath is the developer the second bath is the activator. As noted by Gerald the film speed is locked in, change in temperature or extended time in the first or second bath does not change the outcome. When I was a working PJ in the 70s I always carried a quart kit of Dinafine with me for emergencies or if I needed to push Tri X to 1600. Hard to beat in the field, not temperate sensitive, 3 mints in part A, 3 mints in B, no stop bath, rinse, fix, wash, rinse in distilled water, and dry. When using Diafine I shot plus x at 400 as my standard film. When I moved to Phoenix in the 80s I used Diafine in the summer has my tap water was running around 90 degrees, developed my film at the temp of my wash water. I now have a chiller for wash and have not used Dinafine in many years. It provides fine grain and low contrast so I printed at grade 3 or 4. I recall someone who said he pushed Tri X to 3200 by running the film through twice, after a long wash, no fix then back into bath A and again in bath b for the recommended time. I have not attempted. Thin films like T max have lower EI than older films. And never never allow part b to get into part a.