another way to ponder 'intermittent' agitation

albada said:

The OP is proposing using a fixed number of agitations instead of a fixed time-interval.
My knowledge of chemistry is rudimentary, but this makes perfect sense to me.
If a chemical reaction only proceeds half as fast and thus takes twice as long, then doubling the time-interval (giving the same number of agitations) will produce the same result as double-speed and half-interval.

However, the rate of diffusion through gelatin does not depend on dev-rate, so that complicates things.

Anyway, I have created a concentrate giving XTOL-quality, and I designed it to have twice the dev-time as XTOL. And I recommend agitating every 60 seconds instead of Kodak's recommendation of every 30 seconds. It's worked fine in my experiments.

Mark Overton

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Mark,

Just a couple of thoughts here:

First, the time between agitations is long enough to allow the developer to exhaust in areas of greater density (compensation) should be fairly constant for a given film/developer combination.

Now, if you want a compensating effect, you need to make sure the time between agitations is long enough. It would seem to me that this time would be longer with a more active developer than with a less active/weaker one. Therefore, to achieve a certain amount of compensation, one would have to increase the agitation intervals for the more active developer, not decrease them as the OP is suggesting.

Similarly, for weaker developers, the interval at which a certain amount of compensation occurs will be shorter. Therefore, for a given amount of compensation, one would have to increase the frequency of agitation compared to a more active developer, not decrease it.

Of course if you don't want and compensation, then just agitate away, it shouldn't make much difference at all as long as the agitations aren't long enough for developer to exhaust in the highlights; any agitation scheme that accomplishes this would yield the same results as long as development time was appropriately adjusted.

Best,

Doremus

Kirk Keyes said:

Has anyone mentioned "diffusion" yet? (Doremus used "infuse"...)

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... and should have used "diffused." Although the "stronger" less-exhausted developer in a low-density area moves into a bit of the area of higher density much like tea infuses into hot water, I think the better technical description would be "diffusion from areas of high concentration to lower," or something like that. I stand corrected.

Best,

Doremus

Doremus Scudder said:

Still, in my book this means being able to get (squeeze) more usable information into the printable density range of the negative.

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The point I see many people miss is that the paper defines the range that prints straight and easy from the negative.

markbarendt said:

The point I see many people miss is that the paper defines the range that prints straight and easy from the negative.

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Absolutely! Thanks for clarifying.

Basically, what I am saying is that compensation allows a greater subject brightness range to be squeezed in to the density range of the negative that will print well on a particular contrast-grade paper. I need to be more precise when I express such things so as not to add to the confusion.

Best,

Doremus

Michael R 1974 said:

To clarify it slightly, I'd prefer saying it allows a greater total subject brightness range to print straight on a particular contrast grade.

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The compression occurs in the highlights, so shadows and midtones will have normal gradation.

Suppose you want the opposite. Suppose you want compression in the shadows, with normal gradation in midtones and highlights?
Underexpose, and/or use a film with a long toe.
That will also compress a wide image-scale to fit the paper.
It depends on where you want the compression.

Mark Overton