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This should not, however, lead to an attitude of satisfaction with our present status, which does not provide a dependable instrument or method to correctly calculate total visual contrast or its components in the object. Regardless of artistic satisfaction, there are many occasions when an accurate knowledge of visual contrast relations would be most helpful, for instance, when pictures are made on location over the length of a full day or of several days which might mean a very noticeable and undesirable change in brightness contrast in the object due to the shifting of the sun or to the natural change in sky conditions.
Before dealing with the possibility of solving the problem of determining visual contrast in relation to photographic reproduction, it is necessary to point attention to the fact that this problem can be considerably simplified if whenever possible the negative exposure level would be raised to a point which would guarantee rendering of all negative densities on the straight-line portion of the characteristic curve. The high speed and wide latitude of present day negative material permits this full exposure under the majority of light conditions. Thus, it is evident that, dealing with linear contrast relations only, the problem is appreciab'y simplified, at least as far as the negative is concerned. In the positive print, however, it becomes essential to place part of the reproduction in the curved-toe section to permit rendering of sufficient transparency in the highlights fora faithful reproduction of the overall brightness level.
Film Characteristics
The photographic characteristics of positive film being used at present in professional motion picture work are to a large extent standardized. There is little appreciable difference in speed and slope between the competitive types, and this is very gratifying to the laboratory as it permits establishment and maintenance of constant conditions in printing and printing equipment.
Th e same uniformity, however, does not prevail in the various negative products offered to the market. The reason for this difference is that the principal characteristics required of negative material cannot be perfected in the manufacturing process without the partial sacrifice of other characteristics. Furthermore, with very little exception, a single all-round negative type has been used for general photographic work since the introduction of the Panchromatic Superspeed type, while the variety of problems and tasks to be solved and performed could easily absorb several types of negatives with marked difference-, in photographic characteristics.
The laboratories processing the negative and print could reasonably ob:ect to such variations in negative film, as the existence of such types demand special handling of each type in development, which, of course, would present difficulties in view of machine deve'opment. As most laboratories are using single strand machines, it is not impossible to change deve'oping time in order to secure ideal conditions for the rendering of proper contrast in different film types, as this is practically done at present in all laboratories which prefer and emp'oy the test system" to the "time and temperature system."
I To Re Continued )
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