I have followed this thread with a great deal of interest. There seems to be an awfully lot of "black magic" and very little of sensitometry as I observe some of the people who expose film for and then print it on Azo paper.

In the midst of all of this confusing information I decided to conduct tests of the materials to see what the materials themselves indicated. I began these tests with the paper using a reflection densitometer exposed to a known density in the form of a Stouffer calibrated step tablet. My reason for doing this was that the Azo paper is a fixed grade material and for that reason it's sensitometric performance is fixed.

What I found was that Azo grade two has an exposure scale that will accomodate a negative of 1.60 density range (high value density minus low value density and not minus film base plus fog). I found that grade three Azo will accomodate a camera negative having a density range of 1.10.

The matter then becomes one of selecting a film and developer that will produce a density range that matches the paper. Not all films are equal in this respect. Furthermore not all of the same speed from differing manufacturers are equal in this respect. There is one way to know the film's characteristics and that is to test the film. Everything else is hearsay, rumor, and rethoric.

When some people indicate that they are rating a 200 speed film at an EI of 100 and placing their shadows at Zone IV and then further state that this indicates a two stop decrease in speed from the mfg rating I find that I must question their reasoning. This doesn't represent a two stop decrease but rather a four stop decrease from the manufacturers rated speed. If the film exposure breaks at Zone three then the film is incorrectly rated.

When we move the lowest values four stops up the characteristic curve of a film what happens is that we move the entire exposure up the curve. This would not be a problem except that film curves for the most part have limited straight line portions to the curve. In the case of a four stop overexposure we would place our highlights on the shoulder of the curve. This leads to poor highlight separation at the expense of better shadow separation. This is further complicated by the fact that the compressed highlights located on the negative's shoulder are then placed on the toe of the papers characteristic curve. This serves to increase the compression of highlight tonal scale still further.

Additionally for those who use staining developers the beneficial stain aspect of a camera negatives density is proportional. What we find in this consideration when film is overexposed is that the stain density is further compressed from what would be the case in a properly exposed negative because we have a higher value in our low density to show the stain density effect.

I have no argument with those who wish to expose film in whatever way that they choose. I just don't buy the fact that the rules of the sensitometric characteristics of film, film developers, and paper have somehow been magically repealed.