British Kinematography (1951)

June, 1951 13UDLEY : STEREOSCOPY IN THE TELEKINEMA 179 definition with the two components fused binocularly will be only 50 per cent, of that obtainable with a s'ngle, planoscopic picture occupying the whole frame. This is a topic which the author has had cause to examine with some thoroughness, and it is to be emphasized that if the two components of the stereogram be projected and viewed as a three-dimensional image of given size, then the definition will be almost precisely equal to that of the image of the planoscopic picture projected the same size. The word almost is used because there will be a very small, imperceptible reduction in definition attributable to the stereoscopic image, which reduction varies inversely as the total area of emulsion occupied by the component pictures, and directly in accordance with a very complex function of the number (two in the present case) of such pictures. The complexity of the direct function is due in part to the fact that the homologous views with which we are concerned in stereoscopy are not precisely the same except when the object is at infinity, the dissimilarity increasing with decreasing distance of the object. For all practical purposes, however, the definition available with a simple stereogram can be taken as dependent on the combined area of the two views — not on the area of a single component. An interesting series of tests was carried out some time ago to determ'ne the number of identical pictures which could be recorded satisfactorily in a single 35 mm. frame, these images being projected in accurate superimposition. The superimposed images were compared with a single image, projected to the same dimensions, of the same subject photographed full-frame size. For reasons which need not concern us here, these comparative tests were made with frames so divided that the number of pictures was successively 2, 22, 23, 24 . . . and so on. It was found that even with 26 (i.e. sixty-four) pictures per frame the reduction in definition was surprisingly small. Telekinema Two-film System As we have seen, for one reason or another decisions were taken against adopting for the Festival of Britain Telekinema stereoscopic films any of the processes so far discussed. There remained, therefore, no alternative other than to employ, in the most effective manner possible, the w7ell-kno\vn polarized light process involving the use of two cameras and two projectors. It is not without interest to note that this method was proposed as long ago as 1890 by Anderton, but the development of a practical process was delayed for nearly half a century by the high cost of natural polarizing crystals and the difficulty of obtaining them in sufficiently large sizes. E. H. Land, in 1934, went a long way towards overcoming these obstacles by his invention of the synthetic polarizing material which, of course, we know as Polaroid. The Festival of Britain, when placing the contract with Stereoptics, Ltd., for supply of the necessary stereo photographic apparatus, laid down a rigid specification as to not only the precision with w7hich the equipment must be manufactured, but also the functional characteristics of the apparatus. The more important of the functional requirements are listed below: (1) The complete apparatus, including two Newman Sinclair Model G Auto Kine camera?i provided for the purpose, to be sufficiently light to be supported by a single Vinten tripod. (2) The apparatus to be suitable for use with matched pairs of Cooke lenses ranging in focal length from 28 mm. to 100 mm. (3) The effective stereoscopic base of the apparatus to be adjustable from a maximum value of not less than about 8 ins. down to a minimum value rather less than the normal interocular distance. (4) The angle of convergence of the optical system to be adjustable independently of the stereoscopic base. (5) The camera mechanisms to be operated synchronously. (0) Focusing of each pair of lenses to be coupled and synchronized, so that adjustment of the focus of either one of a pair of lenses produces a corresponding adjustment of the focus of the other. Stereoscopic Camera Equipment The apparatus developed in order to meet the above requirements is illustrated in the photographs Figs. 9 and 10, which show respectively front and rear views of the equipment. The principle involved, which is the