[pure-silver] Re: re-using DDX


----- Original Message ----- From: "Shannon Stoney" <sstoney@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, March 31, 2006 12:10 PM
Subject: [pure-silver] Re: re-using DDX


>

I'll try that. What do you mean by minimal agitation? My normal
agitation is 10 seconds once every 60 seconds, as per Ilford's
directions.


That's fine with LF. The minimal agitation is more important with 35mm and I
forgot that you are exclusively LF (aren't you?). I use 12-13 min for TX or
TMY and it come out fine but, DON'T REUSE IT. It has compensating effect at
this dilution so you will probably see no more blown highlights. The gamma
will be a bit lower but I think you'll like the tonal range.


Right now I'm processing some MF film: HP5+. I like a long scale. The paper scale with the enlarger I use now, and my last few boxes of Agfa paper, is about 1.3, I guess because of the diffusion head.

So for MF film, what would minimal agitation be?

--shannon

Shannon, the idea of "minimum" agitation comes from the idea that a highly diluted developer becomes partially exhausted in the highlight areas where it develops the most silver. This exhaustion is supposed to reduce the amount of development there resulting in lower contrast highlights. Under some circumstances this can work but in general lack of agitation results in uneven development. To get the best results from a compensating developer it must really be used with stagnent development, meaning NO agitation. This also requries the film to be horizontal so that there are no directional effects from diffusing reaction products causing convection.
The degree of development is partly dependant on the amount of agitation so, if the charts supplied by the film or developer manufacturer are to work the agitation method specified on must be followed. Other agitation methods can be used but there may be some descrepency in the contrast predicted by the time/temperature chart.
Acutance is a very small scale effect causing an effective increase in the contrast at the borders of high and low density areas. It is caused by diffusion of reaction products laterally through the emulsion. Because the diffusion path to the surface of the emulsion is often longer this effect can occur to some degree even when the film is agitated continuously. For the most part acutance effects are due to a combination of the developer and emulsion properties.
As far as "scale" nearly any film will record a much longer scale of brightness than can be printed on a reflection print. I don't know of any modern film which has a real "shoulder" on its curve unless exposed many stops beyond normal. The idea is to expose and develop the film so that the the range of tones recorded on the "normal" part of the film characteristic curve are sufficient to give a fairly linear reproduction of the mid-grays in the scene. This is what the eye expects to see. Lowering the contrast of the highlights will result in "blown out" highlights because the result is too low contrast there to satisfy the eye. Burning in, either manually or by masking, is about the only choice if you want to have a reflection print which gives the illusion of a longer brightness range than it is capable of.
Overall contrast of a negative is controlled by choosing the development time. Once this is done the effective film speed can be determined which will put the minimum brightness point of the scene to be photographed onto the toe at a point where its contrast is high enough to yield sufficient detail. This must really be worked out experimentally although its made easier by the fact that B&W film has a very large latitude for overexposure. By latitude I mean that the range of exposure which produces the same tone rendition on the print.
The difference between a diffusion printer and a condenser enlarger of the usual partly diffusing sort (Omega, Bessler, etc.) is about one paper grade difference for the same negative. This is _exactly_ compensated for by choosing the paper contrast grade appropriately. One can also choose to vary the negative contrast so that negatives will print on Grade-2 paper. This is done by adjusting the development time and exposure.
I think you should try conventional means of development and agitation before experimenting with "compensating" type developers.
Iford and Kodak agitation, while different, are very similar in their effect on development, I don't think it makes much difference in results.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 

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