Movie Makers (Jan-Dec 1952)

77 STEREO STRIDES ONWARD Latest in the march of stereo movies, the Nord 3-D system is analyzed by its inventor ROY A. CLAPP, Design Engineer, The Nord Company SINCE it is no secret that within the past few years stereoscopic still photography has gained a tremendous number of enthusiasts, it should be good news indeed that anyone with 16mm. cine equipment can now make and screen true stereo movies. Two new optical devices, the Nord 3-D (three-dimensional) camera converter and the Nord 3-D projector converter, make this interesting development possible. The camera unit differs radically in principle from anything heretofore available; and I believe that MoviE Makers readers will be interested in its design. Basically, the unit employs optical glass wedges through which the light passes and, by the bending action of these prisms, a pair of stereo images are formed. Fig. 1 illustrates the schematic principle involved. A pair of large wedges, made of crown optical glass, are located a considerable distance in front of the camera lens. Between these large prisms and the camera lens are another pair of wedges of opposing form but with a weaker power due to a smaller angle. This second pair of prisms are made of flint glass, and their angles are so calculated that the combination is color corrected just as are modern camera lenses. The effect of these optical elements is to produce a dual set of images, in which one corresponds to a view as it would be seen by the right eye, the other to the same view as seen by the left eye. Together these twin images produce a stereo pair. But if these light-bending prisms were laid out as shown in Fig. 1, the path over which the light rays must travel would be impractical as to length. For convenience, therefore, in mounting this optical system in front of a camera, the light path must in some way be compacted, or folded up. How this is accomplished, by interposing along the pathway a large lower mirror and a small upper mirror, is plotted schematically in Fig. 2. Finally, how . LARGE CROWN PRISMS .CAMERA LENS SMALL FLINT PRISMS MIRRORS FOLD THIS DISTANCE UP FIG. 1: The basic optical system of the Nord 3-D camera converter is diagrammed above. Light passes thru two prisms to record stereo pair. There are, probably, scores of thousands among today's teeming, teen-aged camera toters who believe that stereoscopic photography was born but recently with, say, the advent of the Stereo-Realist camera. Nothing could be further from the truth — as the parents and grandparents of these precocious button pushers can well testify. The principles of stereoscopy, as any reference work will tell you, were first understood by Euclid in about 300 B.C. Little application of these principles, however, seems to have been made until the 19th Century when, in 1838, the first true stereoscope (using paired drawings,) was announced. Early in the following year, Daguerre donated his sensational photographic process to the French government, and by 1844 stereo-photographic images were in use. Stereoscopic pictures in motion (calling even then for special viewing spectacles) seem to have appeared around 1880. Since that time the developments in stereocinematography have been many and varied. As the latest among these developments, although not necessarily the last, Movie Makers presents a discussion of the recent Nord 3-D system, prepared by the design engineer of the project. — The Editors. this entire optical train is housed in the Nord 3-D camera unit, is diagrammed in Fig. 3. In use it is only necessary to position the optical head in front of the camera lens. The unit is held in place by a universal bracket. The camera attaches to this bracket in exactly the same way it would be mounted on a tripod, so that it can be instantly attached or detached as the occasion requires. Further, the bracket is universally adjustable, so that with the aid of a screwdriver it can be lined up with any make of camera. Also, since the unit does not attach to the lens itself, there is no problem created by the speed or make of lens used. In focal length, however, the lens must be the 1 inch optic that is standard to all makes of 16mm. cameras. For, since we are trying to depict distance relationships as accurately as possible, neither the wide angle nor any telephoto lens is suitable for stereo filming. The reason for this is that the intended function of these lenses is to distort normal perspective. [Continued on page 86] SMALL MIRROR SMALL PRISM (FLINT) HOUSING LENS FIG. 2: Long path of prism-bent light rays is compacted as above by the lower large mirror and upper small mirror in the working design. OPENING "LARGE MIRROR 'LARGE CROWN PRISMS FIG. 3: Actual housing of the 3-D optical system is in dark outline. The unit is positioned in front of camera lens on a universal joint.