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Fig. I. Methods of producing the Picture on 16mm. Film.
means now employed. The original sound source, either through a microphone or off a disc 1 or other recording, can be recorded directly on to the final print, if only a single copy is required. Alternatively, a 16mm. duplicate negative may be made, and the prints taken by contact printing. From a 35mm. original neg itive, the sound may be reduced optically on to a 16mm. print, or, from a 35mm. print, a 16mm. negative may be made optically, and subsequent prints made by contact printing. Another method introduces re-recording from 35mm. positive. This has the advantage of making it possible to introduce frequency correction, in order to compensate for loss of higher frequencies, due to the low linear speed of 16mm. running. It is also desirable to cut off frequencies above 6,000 cycles per second, in order to minimise cross-modulation troubles. In some cases, 35mm. film is re-recorded on to 35mm. in order to obtain a frequency-corrected negative, from which optically reduced prints are made. From a positive print of a frequency-corrected negative, an optically reduced 16mm. negative could be printed as described above, and contact prints of this negative would then be made.
Any of these methods may be used with any of the picture production methods already outlined, and it is obvious that unless a very careful balance has been achieved, serious difficulties will soon arise.
The Requirements of Processing
Modern high-speed developing machines handling release prints can only be run economically if the balancing of the different processes has been done at the various printing and negative stages, since, unlike still photography, with its various grades of paper, kinematography has only one final positive material. It is, therefore, important to consider the possibilities and requirements of the final prints, and adjust the preliminary processes accordingly.
The requirements of a print are that it should reproduce on the screen a faithful rendering of the original subject in tone values. The determining factor of the quality of a print is therefore its contrast, the measurement of which is made by means of sensitometry. The curve (Fig. 3) is steep — that is, the gamma is high.
This print must have been made from a negative, and Fig. 4 shows a typical negative curve from which such a positive might have been printed.
Negative and Positive Gamma
Comparison of Figs. 3 and 4 will show the essential difference between the positive and negative gammas. On the positive curve, any difference of exposure, as plotted on the exposure axis, is increased by the gamma (2.5) if plotted against the density axis, owing to the angle of the straight line section. The tangent of this angle is gamma.