Science: Stereoscopy

At last month’s meeting of the British Association for the Advancement of Science (TIME, Oct. 5), Dr. Robert T. A. Innes, astronomer, indicated that he has been able to produce stereoscopic effects on the cinema screen. Last week the foremost U.S. authority on the subject, Dr. Herbert Eugene Ives of Bell Telephone Laboratories, showed the Society .of Motion Picture Engineers at Swampscott, Mass, why stereoscopic cinemas were yet impossible in practice.

When a person looks at something, he really sees two different views. The right eye does not see exactly what the left eye sees, and vice versa. The brain combines the two scenes into a composite. Thus a person sees objects in relief, in the round.

The old-fashioned stereoscope does what the living eyes do. A camera with two lenses makes two slightly different pictures. The pictures are carefully mounted side by side on a card which is placed before a pair of lenses fixed on a frame. The left lens shows only the left picture to the left eye; the right lens only the right picture to the right eye. The brain combines the pictures as solid effects.

The cinema can do the same. But the difficulties of serving large audiences make the showing impractical.

Already tried out with little satisfaction have been:

1) Showing the left and right pictures simultaneously or alternately. A person by straining his attention can learn to focus each eye on the proper view. Or, if he sits at a certain focal distance and angle from the screen, he can look through a stereoscope. Or he can hold a mechanical pair of lorgnettes before his eyes. The lorgnettes, which John Bellamy Taylor of General Electric used over 20 years ago, have shutters which rapidly and alternately blink the view of each eye. Viewing devices with special lenses, mirrors or prisms also permit stereoscopic effects. But each person in the audience must have a special pair for his seat.

2) Another method is to make one stereoscope view through a green filter, the other through a red filter. On the screen the two pictures overlap as one confused scene when looked at with the unhelped eyes. But spectacles with one red glass or celluloid lens, and the other of green, resolve the confusion, give the impression of a picture in grey and white. This method has been tried out in theatres. It is clumsy.

3) Still another method is to take the separate views through light-polarizing camera lenses, throwing the combined scene on a special, non-diffusing screen, and viewing it with special glasses. This method too is impractical.

Dr. Ives has worked out the problems of another method, which requires no special glasses or effort for the observer. He calls it “parallax panoramagram.” An object is photographed from many points of view through a grating. The grating deflects and breaks up the image on the negative. The positive print is a blur unless viewed through a grating the duplicate of the camera’s. Still pictures made and scanned this way are brilliantly realistic.

Moving pictures may be made through a similar screen. But the cameras must be run much faster than they now are. There must be many cameras focused on the same scene, and many projecting machines throwing the images on the screen. Screens must contain minute ridged reflecting and refracting elements of “extreme optical perfection,” so that every person in the audience may see every aspect of the picture. Projection lenses must be of “extraordinary defining power.” The films must run through the projectors with microscopic precision. Finally, if all the mechanical requirements are accomplished, there remains one more obstacle. No photographic chemicals are yet known which will register pictures as swiftly as Dr. Ives’s parallax panoramagram method requires.