Fast black and white films have a mixture of grain forms and grain sizes, chemically correct salt crystals. Silver salts. There are also different silver salts, namely bromide and a little iodide. In some cases nitrates, too.
The crystals are partially veiled inside, meaning that there is already some genuine silver in them. The future developed silver will deposit on those germs. In strongly exposed areas all salts are affected and decompose. In weakly exposed areas only the highest sensitive salts get affected. From these chemical differences we find the film reacting not in exact lineal fashion but rather as sort of an S curve when plotted. The curve’s toe and shoulder show that the differentiation of shadows and higher lights is limited by the physical and chemical facts about those crystals.
A negative’s information will be put onto another film stock, again a non perfect emulsion with limited differentiation at the extremes, but the positive emulsions work harsher, with stronger contrast, and develop a higher maximum density. According to the Goldberg condition a neutral or perfect image contrast is the product of negative and positive contrast. These are laboratory issues whose task it is to produce projection prints that display a nice image. Lab technicians need to know an average Albedo of cinema screens and an average brightness level, else it is impossible for them to determine the contrast and the mean density of prints. In other words, calculating backwards from a theoretically perfect image on a white screen of 100 percent gain the prints’ contrast and density are defined. The Callier effect comes also into play with the projection lens and illuminating system, pushing print contrast to a Gamma of about 1.55.
Small gauge film projection happens often with lesser screens or in not completely dark surroundings, thus an 80 percent gain is generally assumed. Lighter but a little more contrasty prints are needed. Portable projectors’ optics are also different from commercial cinema’s arc lamps.
In order to judge on your work, you want contact positives off your negatives, presented under about the same conditions as are expected with the majority of theatres. Do you see how complicated matters are?
You cannot discuss photographic qualities by the image on a viewer screen. Your questions aim at the heart of cinema and that has to do with what I’m describing. As a cinematographer you should know that film processing, development of exposed photographic materials, is embedded in a long chain of conditions. Finally, the lighting on set actually is dictated by all the aforementioned factors. Always think of them. Always look on the bright side of life.
Edited by Simon Wyss, 03 October 2017 - 02:14 AM.