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

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mittent or continuous motion. The relative merits of the two systems, in their various applications to television recording are discussed by Kemp (loc. cit.), and there is therefore no need to enlarge upon them here. It must be noted, however, that Kemp's approach to the problem is conditioned by the fact that his treatment concerns the problems of recording broadcast television, where the worker is presented with a composite signal intended for reception on a normal television receiver. The form of this signal is fixed and he cannot in any way vary it. The authors, on the other hand, are at liberty to make any changes in signal waveform that they see fit and consequently their conclusions are influenced by the greater degree of freedom open to them, as well as by the fact that they are working to much higher standards of definition, which in turn bring special problems. Whilst there can be no doubt that continuous motion is exceedingly attractive from many points of view and may prove to be the ultimate solution, the accuracy of registration which can be realized in the present state of development is insufficient for recording pictures of the order of definition required. In consequence, attention has been directed to the intermittent system, which has been proved by many years' use in the motionpicture industry to give a very high degree of accuracy of registration. The application of the intermittent movement to the problem of recording high-definition electronic images has, of course, been greatly eased by the freedom to adapt the signal waveform to suit the operating conditions of the photographic camera. To illustrate the degree of this easement, consider the case of recording broadcast television with an intermittent camera. If the maximum picture information is to be recorded, the film shift must take place completely within every other frame-suppression interval. This means that the film must be accelerated, decelerated, brought to rest and registered in a period of 14 television lines, which represents a time interval of about 1.4 millisec, or 12° rotation of the filmcamera mechanism. Expert opinion indicates that a film shift of this speed is on the limits of possibility, and that even if improved design enabled it to be realized, the strain on both film perforations and mechanism would be such as to make frequent jams and stoppages unavoidable and to render maintenance extremely difficult and costly. No such mandatory condition exists in the requirements of the proposed system of high-definition recording, and it is possible to choose a frame-suppression interval of any length desired. Any increase would, of course, be made at the expense of the time efficiency of the system, i.e. the ratio of the time during which information is passing to the time during which the system is inoperative during suppression. Nevertheless, a useful compromise may be struck in which the gains accruing from the use of a longer frame-suppression period outweight the loss in terms of time efficiency. As stated earlier, the use of sequential scanning gives a substantial gain over interlaced scanning, since there is only one frame-suppression period per frame in the former as against two in the latter. The authors, therefore, advocate an intermittent camera with an accelerated film-shift operating during the framesuppression period. (6.2) Exposure Time and Movement Blur: Some consideration must be given to exposure time in an electronic, as opposed to a photographic, camera. In normal motion-picture work, the maximum available exposure is usually 180°, and although practice varies, the usual run of pictures is shot at full exposure. Shorter exposures, obtained by reducing the shutter-opening angle, are generally used only for scientific investigations. 456 December 1952 Journal of the SMPTE Vol.59