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Re: Pyro Developers Question.From: dickburk@ix.netcom.com (Richard Knoppow) "Darkroom User" <Darkroom.User.6a42d68@photobanter.com> wrote in message news:Darkroom.User.6a42d68@photobanter.com... Well, finer grain is open to the question of how that was determined. Lots of developers yield finer grain than D-76, some modern ones, notably Xtol, also deliver somewhat higher speed but most fine grain developers loose some speed. Pyrochatichin, which is related to pyrogallic acid but is a different chemical can be used in developers which have strong edge/border effects. This gives the illusion of sharpness. There is another effect of certain developers containing pyro and its relatives, that is that it tans the gelatin image wise. The variation of index of refraction after development can lead to a similar kind of edge effect which is visualized as "acutance" or the impression of sharpness. Note that "acutance" is a Kodak term for this illusion. High acutance films do not, in general, increase resolution, in fact they may reduce it. However, where one is working with small negatives acutance effects will partially compensate for the lack of sharpness in the lenses. Note also that border/edge effects, and hense acutance, is of a fixed scale so that its effect is dependant on the magnification of the image on viewing. It can have a quite significant effect on 35mm negatives but will be virtually invisible on a 4x5. Graininess also gives the illusion of sharpness. A somewhat blurry image when overlayed with a sharp grain pattern will appear to be sharp, at least at first. -- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com
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