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

mate audience to experience; the stereotechnician will then be able to tell them how that effect can be produced, provided that the camera equipment is sufficiently flexible and that psychological viewing factors are properly taken into account. A true parallel, therefore, would be with the science of sensitometry, which does not attempt to prescribe fixed exposure settings, but does in fact analyze the consequences of making toe and shoulder exposures, altering the developing time, using different types of emulsion, and so on. In the same way, a valid transmission theory will enable the stereotechnician to determine what will be the geometrical form and position of the space image under all possible camera, optical printing, projection and viewing conditions. The effects of altering the space structure of the image in passing from shot to shot, as well as the space distortion in individual shots, which are revealed by this analysis, will be evaluated in the light of previous experience in seeing 3-D films. Not only will the members of the production team themselves become increasingly sensitive to the appearance of a new kind of film image, they will come to know what is and what is not effective in terms of audience response. Already a substantial body of production experience has been built up in the last two years in the course of developing and applying the principles outlined in this paper. A dozen films have been produced which have been commercially exhibited in half as many countries and seen by audiences now nearing the 3 million mark. If the full possibilities of the 3-D medium are to be exploited, the design of new cameras should be put in hand forthwith. Both theoretical analysis and experience point to the need of a wide flexibility in the tc and h variables, and of a precision of adjustment and film registration equal to that which must be attained in 3-strip color cameras. By using separate 35mm films for the left and right-eye images, and by interposing the minimum number of additional glass surfaces between scene and film, these requirements can be achieved, though there is at present only one camera in the world (the work of J. A. Norling) of adequate precision and flexibility. Granted adequate cameras, there is no reason why films as ambitious as any now made in Hollywood should not be undertaken in the vastly more powerful 3-D medium. The knowledge thus acquired of production problems and audience response would remain of undiminished value were polarized projection to be replaced in the future by some type of integral or "free-vision" viewing screen; for though the means of separating the images may change, their appearance in space is likely to remain unaltered. For example, the parallax barriers recently classified by Kaplan in a paper of fundamental importance,12 one and all give rise to an image geometry identical with that already analyzed in Part I for a pianostereoscopic system. As long as audiences will, therefore, accept for the time being the slight inconvenience of glasses — which recent European experience seems to bear out — there is no reason why major studios in the U.S. and Britain should further delay the production of at least a few dramatic films to determine whether or not they are the answer to a declining box office. At the same time, other developments in the projection field will be under way, which will still further close the gap between the spectator and the scene, and will reinforce that sense of participation in the drama of a film which alone, perhaps, can prevent the great audiences in the motion picture theaters from dissolving away into little audiences in front of home television screens. Spottiswoode, Spottiswoode and Smith: 3-D Photography 285