increase/decrease development with divided developers?

This is kind of a theoretical question because I have never tried a divided developer.

As I understand it with a divided developer like Diafine the degree of development is basically built into the process, so you can't really push or pull a film relative to the base performance of that film in the developer. However, could you push or pull the process by using a different concentration of the first solution, the one that holds the developing agent? (I will call this solution the "loading solution".)

It seems to me that the degree of development is primarily determined by 1) what chemical is used for the developer in the loading solution (controllable, but for sake of discussion let's not vary this), 2) how much developer is loaded into the emulsion (controllable by the concentration of the loading solution), 2) the diffusion rate of the developing agent out of the film when the film is placed in the alkali solution (not controllable).

There are probably some secondary factors as well, such as what is the diffusion time of the alkali into the emulsion after the film is placed into the alkali solution (not really controllable, but probably fast enough to make this a minor variable), what is concentration of the alkali (controllable), and localized developer exhaustion or bromine build up in the highlights (probably not controllable).

Out of these it would seem that altering the developer concentration would provide a good way to push or pull the film. If so, imagine keeping several stock solutions of loading solution, each at a different concentration. Then you could push/pull film at will with divided developers.

A follow up question on this topic: I understand that Diafine tends to produce flat looking low contrast pictures. Could you use the push process scheme outlined above to increase the contrast with Diafine, probably combined with reduced exposure?

Thanks.

Alan;

Divided developers with an A - developing agent and antioxidant and B - alkali part, are very very touchy. The reason for this is that films vary in silver halide content and in thickness (gelatin content and hardening). For this reason, what works with one film may not work for another. What is worse, age of the film can be a factor as hardening often continues after manufacture.

So, as a result, you have to do more work fine tuning a given film to the times in A and B to get the desired result. And, if the film is 'improved' its behavior will change in a 2 part developer.

My experience with them has been rather offputting, and so I tend to stay away from them, and I'm sure I'll take a lot of flack over what I have just said, but it is a fact of chemistry and physics that you have to contend with here.

I've found I'm better off by combinging the A + B parts and using a single bath development.

I know that there are advantages claimed, but IMHO a single part highly diluted developer has performed better and is more repeatable across products than a two part developer.

PE

What PE has said is true, and we all have our favorite devs; some work for us, some don't.

I've played with all the divided devs in "The Darkroom Cookbook" and "Film Dev. Cookbook" with some success. It is thought that films of today have very thin emulsions and just do not soak up enough of the "A" bath to get a fully devved neg. WD2D in TDC is one that I've had good luck with. The "B" bath contains a goodly amount of carbonate and that seems to get whatever amount of "A" bath soaked into the emulsion to work.

Another divided that can work is Barry Thornton's. He decribes it in his book, "The Edge of Darkness" . You may also find the formula here or do a google. However, it's also a worthwhile book to own.

If you'd like to get into divideds, be prepared to do lots of testing and put up with failures along the way.

As far as pushing and pulling go, I'd say no. The process is just too simple to be played with. "A" bath gets soaked up by the emulsion, "B" bath get it to work. That's it! You can change to a different dev, but I would say that you couldn't just "change the times in each bath" to do much.

I think Jim has made a very important point here. The developers of this type cannot be played with. They just have one button (on-off). They absorb the maxiumum amount of A and then go to work in B until A is used up. It gets much more complex if you try to push or pull the conditions.

PE

If the first part is truly inactive until the second part is added, then there is not a lot of control by timing. There is the possibility of varying the concentration of each part, so you might keep two different concentrations of each. I used divided developers a lot during one period when I had difficult (or so I thought) stage lighting conditions. Then I made a densitometer and started measuring everything. The compensating effects of divided development should show in those characteristic curves, right? Nope. Not enough to make it worth the rigamarole. I can't say I tried every possible combination of A and B, but I tried a bunch. You'll have to try it for yourself, but when you do, remember to compare results with a single solution developer having the same chemicals to see if you really get the difference you expected.

Agreement?

I don't know how this happened. I should have started with the original post. Instead, I find myself agreeing with what PE said. How can that be?

An historic first, perhaps??? )

Actually no, but when we do agree, you had better listen.

PE

I agree with PE more than it would seem. I do always read his posts, not to find out what he thinks of me but to find out something new about photography. We have had arguments about how accurate one must be in measurements of chemicals, and whether one could ever be accurate enough with a set of measuring spoons, and whether heating chemicals in a microwave oven could be safely done, and have sometimes presented different viewpoints on a subject that I hope clarify the whole picture rather than obfuscate. As I said once, if we occupied the same office space we might sometimes go at it rather heavilly in the process of solving one problem or another, but that's part of the fun of research. If two people can't argue with one another, then there's no problem and they should go out and find one to argue over.

When I seem to be bragging about the many different things I did, it's only to show that everyone was in the same boat. We didn't all do the same things when we worked together on a research project at NASA, but we worked together on the same problem, sometimes two of us, sometimes the whole branch and then some. I don't know how it is now. In those days there were no true engineering specialists. What we were supposed to have learned in any engineering course, any science course, in fact any academic course was how to learn. One of my early tasks was to analyze some wind tunnel data, comparing it with theoretical. I learned more about integration by parts doing that than I did in the college course, but I go it done.

I need to correct a formula in my earlier post. In that post I mentioned a divided dev called WD2D from Anchell's "The Darkroom Cookbook". WD2D is in fact a pyro dev and single solution dev., not a divided dev. The dev in "TDC" I meant to post is D2D by William Davis and IS a divided dev that I've had good luck with.

Sorry for the error.