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Frank --
BTZS methods make prediction and control of image density and contrast relatively easy; a nice bonus is that they can help us control gradation, too. By gradation I mean the relationship of image "grays" to each other, and to the extremes of accent black and white. In designing the "Wonder Wheel" I thought that anchoring a middle value was the way to go, but that allowed both ends of the scale to vary as SBR and development varied, so negative quality was inconsistent.
The time-honored "expose for the shadows and develop for the highlights" is still the best approach for producing optimum negative quality. That pins down Dmin and Dmax, and gradation can be controlled (to the extent that control is possible) by materials' selection. The Matcher portion of the WinPlotter computer program illustrates these middle-value relationships quite effectively, I think. With that program you can simulate the effects that are likely to be produced by pairing various combinations of film, developer, and paper, and watch the middle values slide up and down the scale as you vary such things as film exposure, development, simulated flare effect, and SBR. It's an effective "what if" exercise and quite informative.
If you're not familiar with the Plotter program, download the demo version and try it out. I don't think the Matcher portion is accessible but I think you'll recognize its potential. Incidentally, there's a new chapter on gradation in BTZS 4th.
If I haven't answered your questions adequately try me again.
-- Phil
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