British Kinematography (1952)

May, 1952 BOMBACK : FILM PROCESSING LABORATORY 147 used over the photo-cell when setting the lamp position. Usually, in such cases it is inexpedient to control the lamp brightness through the applied voltage because of the associated change in colour temperature thus introduced. The rate of film travel (factor (c) ) is a function of the printing machine and must be maintained at a uniform value. Here it must be remembered that if the electrical supply is from a fluctuating source any variation in mains frequency will be reflected in varying motor speeds and as such will affect the rate of film travel — and hence the exposure — unless due precautions be taken to offset this effect. Printing machine speeds may be checked by timing the film past the printing gate or more simply by the use of a stroboscope of the repeating highintensity flash variety. Factor (d) assumes importance when the film stock to be printed exhibits more or less reciprocity failure as compared with the film stocks normally handled. As such it can give rise to quite puzzling anomalies in exposure especially when the normal sensitometric tests are made on a time-scale sensitometer. It is also important in the testing of sound recording stocks since the type of exposure given in the camera differs markedly from that of the normal sensitometric equipment. Other factors of importance in printing that call for regular inspection and control are: uniformity of illumination over the printing aperture; accuracy of light changes where resistance control in the lamp circuit is employed; definition of image and the avoidance of slippage in continuous printers, especially for sound, where this may introduce sibilance and " wow," plus a general falling-off in tone reproduction quality. The development of the exposed positive film is attended by all the factors already mentioned for negative film. An added complication is the greater susceptibility of positive film to aerial fog and this is of importance in developing machines where the film travel is not wholly below the surface of the developer solution. The fact, too, that positive film is normally developed to a much higher contrast than negative film means that any irregularities that occur during development through temperature variation or unevenness of circulation will be more readily apparent on positive than on negative film. This should not be taken to imply that control of these factors is not so important with negative film; on the contrary, its importance can scarcely be over-emphasised since any irregularities introduced into the negative film will be greatly magnified in the positive print and wnen once introduced cannot subsequently be removed. Screening. Since the judging of the final print as seen on the screen is to some extent influenced by artistic impressions, it is difficult to provide a standard that will be generally acceptable for all viewers. There may, on the one hand, be the studio personnel responsible for shooting the picture who are anxious to see a faithful reproduction on the screen of trie " mood " they set out to interpret; on the other hand there may well be the limitation applied by the exhibitor who because of his restricted screen brightness level, demands a print some 2 or 3 printer points lighter than these others would be willing to accept. If the audience who pay to see the picture have any views on the matter as well, they are normally, and perhaps fortunately, expressed to some quarter not in direct touch with the laboratory. In theory, at least, the laboratory should be free of the arguments that revolve about this vexed point of print density. Provided due control has been exercised in both the printing and developing processes outlined earlier on, it should be possible to reproduce any given result in all the copies of a particular film within satisfactorily close limits. In practice, however, this is not so, one of the principal reasons being the simple fact that identical prints may appear to be markedly different if the screening conditions are not maintained constant. Thus, for a given size of picture, the projector lamp can affect the result by a change in