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PROCESSING MOTION PICTURE FILM 137
be obvious that a development of high contrast will cause a greater change in density for a small change in exposure than would be the case with a low contrast development. Since the exposure given is controlled in the sound recorder by the characteristics of the sound itself, the range of sound frequencies which may be successfully recorded will be altered by the degree of development given. Finally, the density of the print when no sounds are recorded on the negative, that is, the unmodulated density of the print, is also available for adjustment. As explained previously, the operator has not so much ability to vary the gamma of the final release print since this is set in conjunction with the requirements of the picture.
It is interesting to remember at this stage that the sound is not married to the picture until making the final release prints. We have already discovered the need for making special 'dubbing' sound prints and, naturally, at this stage the sound is independent of the picture and, therefore, positive sound prints are processed to conditions which, whilst they may be unsuitable for the final 'married condition', do maintain a better quality for the intermediate operations. This will be explained more fully in subsequent chapters.
It will be remembered that the current passing through the photo-cell of the sound reproducer is proportional to the light transmitted through the positive print and that this relationship is most easily obtained by study of the transmission-exposure characteristics of the system. Once this has been settled it can be maintained by the normal sensitometric control as applied to pictorial work. One method of obtaining the correct exposure necessary to give the desired transmission is to analyse a family of prints made from sensitometric strips and on sound recording film. However, several possible sources of error must be taken into account if this work is to be of practical use.
When a positive print is being made from a negative it may be carried out in one of two types of machinery. Firstly, it may be made on a machine in which both negative and positive films are held in contact or, secondly, it may be made on a machine in which a considerable space exists between the films, the image from the negative being focused through an intermediate optical system. The resultant density of a print made by the 'contact' process will not be equal to the density of a print made by the 'optical printing' process, even when the incident light on the negative is equal in both cases.
This difference between the two methods is due to the fact that the grains of silver which go to make up the final negative