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

need two eyes in order to construct the depth image at all. Now if a two-eyed observer were stationed at the camera position, the front plane of a given object in the scene would subtend some angle, w, at his two eyes, and the back plane of the same objecc a smaller angle, a/. If co — o}' were not too small an angle for the eyes to discriminate, the object would appear stereoscopically solid. Now suppose this object to be imaged and transmitted to a theater under given conditions. For a spectator of known position and characteristics, the same object will subtend at its front plane an angle 12, and at its rear plane an angle, 12'. The ratio of a small change in the image angle, 12, to a small change in the object angle, co, may be called the binocular magnification, mb, and an expression may be found for it which is analogous to those enunciated above in Eqs. (11) and (12). do) Vt (17) Note that mb is purely a form of depth magnification, having no relation to the width of the image, that it is independent of the value of B, and that (were the two kinds of magnification found to be multiplicative in effect), when B = 0, md = \/mb. Their inverse operation has important practical consequences which will be discussed in Part II. The Complete Theory This short outline of fundamental principles can of course be developed very much further, and its fuller implications are set out in the work already cited.* These shed light on fascinating possibilities of set design which take advantage of the image distortions we have noted, just as the set designer of today makes fullest use of the potentialities of linear perspective. They help to analyze many new techniques in cell and puppet animation. They enable the camera designer to lay down parameters for the construction of professional stereo film cameras. They enable a producer to undertake a complicated studio picture in the confidence that all the problems along the way — titles, optical effects, back projection, stereo windows, and so on — can be surmounted with a full knowledge of what is being done. PART II: PRACTICE It may be that a transmission theory such as this, containing as it must many new terms and concepts, will at first seem difficult to grasp, and perhaps too abstract for the practical needs of film makers. Yet just these objections were made when sensitometry was first introduced as a science. It was puzzling to have to think of densities and gammas and toe exposures when a mere twist of a lens diaphragm had previously seemed to suffice; yet today all these and many other terms are so much a matter of instinct that they trip off the technician's tongue with scarcely a second thought. The practice and nomenclature evolved here for the 3-D film have been carefully worked out with the needs of the professional film maker in mind. Very soon he is just as happy with depth ranges and nearness factors as he is with the rest of the science of film, because he can see what these things mean as soon as he starts to make his first stereoscopic movie. Within the limits of this part of the paper, we shall try to make the reader feel that he is sharing in the production of a section of The Black Swan, one of the many films now completed in accordance with this technique. We shall show how the stereoscopic constants are computed, how film parallax is afterwards determined, how camera errors, if present, may be corrected, and how the image in space finally appears to a member of the audience. The camera on which this film was to be shot consists of the twin assemblv de 264 October 1952 Journal of the SMPTE Vol. 59