Response to id-11 developer

Here's Richard Knoppow's explanation from Pure Silver: The published formulas for ID-11 and D-76 are identical but the packaged developers are not. One big reason for the difference in recommended time is that Kodak and Ilford use different contrast indexes or average contrast to determine the contrast. Kodak bases all of its pictorial film development times on a CI suitable for contact printing. For average condenser enlargers the time should be reduced from 15% to 25% (depending on the film) with a consequent decrease of film speed of about 3/4 stop. Ilford bases its times on an average CI midway between diffusion and condenser times. Plus, Ilford does not use the ISO method for determining speeds. They don't say what system they use but claim their speeds are more nearly practical. Oh, dear; so much for standardisation in the modern world. The CI required by the ISO speed method is actually close to that required for diffusion printing on normal grade paper given an "average" scene brightness range. Lots of room for qualification there. Lots of film makers give times for D-76 these days, but not all indicate what CI they are developing to. Heigh-ho, time to dig out that old densitometer again. ---- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com

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