Journal of the Society of Motion Picture Engineers (1930-1949)

The effect of using a comparatively long exposure of, say, ^g~sec in a photographic motion-picture camera is to produce a measure of movement blur, which is usually regarded as beneficial in smoothing out movement and preventing the formation of discrete separate images of a fast-moving object in successive frames. Picture-goers are used to this effect, and it enhances the impression of movement as portrayed on the screen. In the high-definition electronic camera, the actual time the scanning beam is traversing each picture point is about -£% microsec, or a million-times shorter exposure, since this would be the effective exposure if the camera had no memory effect. Fortunately all electronic cameras have some "memory," and it is possible to proportion the memory to give an adequate impression of movement. In the early days of television broadcasting some cameras had a very short memory, and a fast-travelling ball, for instance, appeared as a line of white dots. An exceptionally long memory, on the other hand, is equally disadvantageous, because under these conditions very serious blurring will occur on moving objects and when the camera is panned. A compromise is therefore necessary, and motion-picture experience indicates that a storage memory of 0.25-0.5 frame in length is likely to be satisfactory. It is not thought that the effect is particularly critical, and most television cameras in use to-day do not show any unpleasant effects in this connection under any reasonable conditions of working. (7) Choice of Film Stock A considerable degree of latitude exists in the choice of film stock for the recording camera, by virtue of the fact that the amount of light emitted by the recording cathode-ray tube is independent of studio illumination and may be kept constant under all conditions. Processing to con stant gamma as opposed to constant density is facilitated by this. Moreover, much more light is available at the film than when it is exposed in an optical camera, not only because the intensity of light emitted by the cathode-ray tube may be made several times that of the light reflected from a studio scene, but also because the optical system used with the photographic recording camera can be made more efficient than that which it is possible to use on a studio floor. Magnification is constant and negligible depth of focus is required, because the cathode-ray screen is a flat field. In consequence, comparatively slow film stocks can be used, with advantage in terms of resolution, rise time, absence of granularity and linearity of tonal characteristic. Moreover, images on finegrain negative are known to suffer proportionately less in processing and printing than those on more sensitive and coarser-grained emulsions. (8) Conclusion Whilst encouraged by the results of laboratory and studio tests to date, the authors are conscious that the paper is necessarily tentative in its conclusions and is in many respects lacking in precise data. However, in view of the rapidly developing interest in electronic filmmaking, they felt that an interim paper of this nature would nevertheless be of interest. (9) Acknowledgments The authors are indebted to: Pye. Ltd.; the J. Arthur Rank Organization; London Film Productions, Ltd.; Eastman Kodak, Ltd.; E. F. Moy, Ltd.; and W. Vinten, Ltd., for information and assistance. The authors also wish to express their thanks to Mr. W. D. Kemp and Mr. B. R. Greenhead for their help in the preparation of the paper. Collins and Macnamara: Electronic Camera 457