Quote Originally Posted by Stephen Benskin View Post
Mark, I was speaking generally. It's a question of what is knowable. Zone System testing defines two points (both mistakenly). Even if they were accurately defined, there isn't any information with what goes on in between. Exposure isn't about that anyway. For black and white negative films, it's about placing the subject luminance range on a part of the film curve that will produce a quality print. There really isn't a correct exposure. That's why Zone System's EIs are usually half of the ISO and the old ASA speeds were half of the current and there's no problem in quality. The primary reasons to keep the exposure as short as possible is to keep printing times a short, limiting grain and light piping, and maximizing sharpness.
The ZS "uses" two locations on the curve to establish the effective speed and to establish a "normal" development target density------in what way are those two points a mistake? Do you mean the value of those two points i.e., 0.1 and 1.3?