Science: Three-Dimensional Movies?

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It takes a sharp, experienced eye to read an aerial photograph, locate targets, measure bomb damage. The picture is flat, looks unnatural because the camera has only one eye and cannot register distance, depth, or solid shape. The third dimension can be added only by double vision, each eye having a slightly different angle on the scene. Such photographs have long been made by double cameras with lenses as far apart as are human eyes. But the production of motion pictures in three dimensions has lagged.

Last week demonstrations by Floyd Ramsdell of Worcester Film Corp. brought nearer the day of movies in depth and color, when the screen will seem to be a stage of unlimited scope. Persistent, inventive Floyd Ramsdell does not use a double camera or double projector, relies instead on a "beam splitter." This mounts two lenses on a single camera, prints the two pictures—one from each lens—side by side in each frame of a motion film. The projector may thus be any standard make but is also fitted with a beam splitter which sets the two pictures almost over each other on the screen.

The result is a blur to the naked eye. To separate the two pictures so that each eye sees only the image meant for it, Polaroid sheets must be used in the beam splitter and also in glasses worn by the audience. Polaroid is a thin plastic containing myriads of tiny, imbedded, needle-like crystals of iodo-sulfate of quinine, all parallel. When a beam of light strikes the sheet all light waves that are vibrating in the plane of the crystals pass through, all others are stopped. Thus the two beams of light from the projector are filtered so that their waves are at right angles to each other. The observer wears similar Polaroid glasses so that his right eye sees only the picture from the right-hand camera lens; the left eye sees only the other picture.

Objects in the foreground are widely separated on the screen. Those in the far background are the same in both pictures. The result is a realistic impression of distance and shape.

Exaggeration is also possible. For aerial mapping a high-flying plane may shoot the same terrain from points a hundred feet or more apart, giving a rangefinder effect as if seen by some fantastic bird whose eyes are that distance apart. When such pictures are viewed by human eyes, less than three inches apart, the effect is one of foreshortening—as if seen from a height of a few hundred feet. Thus reconnaissance has a superb new tool.

For movies one major difficulty remains. All objects must be in focus, no matter what their distance from the camera. This makes the use of large "fast" lenses impossible because such a lens can focus only for one definite distance. With small lenses for universal focus the light must be intense or else the exposure must be too long for motion-picture use.