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Subject: Re: raw 3.1 professional custom profiles for highend digital cameras

"BTW, it's not correct to think of the Zone System pivoting around Zone 5. Were that so, the shadow density would actually decrease with extended development, which is how contrast is controlled."

Ever do a D log H curve? :-) Base + Fog and the toe of the curve really doesn't change with development.

In point of fact, traditional reflected light metering is indeed based upon what later became Zone 5, it's called an 18% grey card. When read by a refelected light meter, this was supposed to place an 18% reflectance as a middle grey on a B&W neg (this was well before color materials).

+ and - processing only changed the slope of the resulting processed tone curve and had a greater effect above Zone 5 than below it. Lower exposure would develop out and not change much even with increased development. But density above middle grey (highlights) would rapidly increase in density with longer development. Hense the ability to alter the contrast of a B&W neg-which was made largely moot by variably contrast B&W papers, which alas, Kodak will no longer be making.

Ever read the book Photographic Sensitometry by Zakia and Todd? I had to, since they taught several of the classes I took at RIT. When Adams developed the Zone System, it was before panchomatic B&W films (they were mainly orthochromatic then) and there was little one could do to alter the contrast of printing papers. That's why he developed the variable contrast approach for negs, which he processed primarily by inspection.

Digital photography with it's linear capture is so foreign to that concept as to make traditional photography a roadblock to learning how to expose digital captures today. And meters based upon an 18% reflectance have less usefulness than spot meters that can measure scene luminance and allow you to determine the scene dynamic range. This will alow you to determine when the scene is within or outside of the dynamic range of the sensor.

You might be surprised at how many scenes are within the sensor's dynamic range. In those cases, increasing the exposure up to the point of near clipping will give a much more controlable and flexible result.

Oh, the curve function in Photoshop bears little or no relationship to tone responce curves in film. . .film had a toe and a shoulder with straight line portions that either increased in slope (more contrast) or decreased in slope, producing lower contrast. But the lines were generally straight except for the toe and the shoulder.

Boy, have we come a long way. . .


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