International projectionist (Jan-Dec 1951)

Diagram of a double projector installation using Polaroid filters on the projectors, plus viewing spectacles. ELECTRICALLY ■ INTERLOCKED OR I WE POLAROID SPECTACLti Pennsylvania Railroad's stereoscopic movie display at the Golden Gate International Exposition in San Francisco in 1940. A Technicolor film, using the stop-motion technique was our next stereo production. A unique filter attachment was arranged in front of the camera lenses. The filters were mounted on wheels which rotated together. Color balance was attained by making sectors having angular dimensions calculated to pass the quantity of light required for each color and as demanded by the sensitivity of the film. The "A" (red) filter passed light to which the film was more sensitive than that passed by the "B" (green) and "C5" ( blue I filters. Consequently the red filter had the narrowest opening of all, and the "C5," to whose transmission the film was least sensitive, had the widest opening. The exposures were made by the alternate frame method of color separation. Three frames, one the red record, one the green, and one the blue, were made instead of one frame as in ordinary photography. These separation negatives were used by Technicolor to make the printing matrices from which the dye imbibition prints were produced. Two Separate Films Advocated It has always been the writer's opinion that the stereoscopic camera for professional use should be built to take the images on two separate films. This is to afford the greatest flexibility in the studio and to permit the use of short focus lenses and to facilitate the making of optical effects in the duplicating processes. One such camera was built. It contains the features deemed essential to a versatile camera. The most important are a variable interaxial and a convergence control, but important too is a binocular finder showing in miniature a three-dimensional view of the scene to be photographed. Visual inspection during focusing seems superior for stereoscopic work and focusing is easier when the view is seen in three dimensions. The binocular view finder has an addi tional advantage: it enables the cameraman to compose the scene stereoscopically, using the interaxial and convergence controls, manipulating them until he gets the best possible arrangement. He can increase the interaxial if he wants to increase the apparent depth of the scene. He can reduce it if nearby objects demand it. The dual projector system used at the New York and San Francisco Fairs is substantially the same as that currently on exhibition at the Festival of Britain. According to press reports, it is also the same system which has recently been demonstrated by Natural Vision Corp. of Hollywood. Dual Images on One Film Systems for stereoscopic films using dual images side by side or one above the other have also been proposed. One of the problems in the two-image arrangement, whether in tandem or side by side, is the loss of light, because the light-covering circle covers a large area around the area occupied by the two images. The ordinary circular light spot from the projector arc spills light all around (Continued on page 28) Natural Vision/ Latest 3-D (?) Entry HOLLYWOOD is currently excited by another seeming palliative for the drooping box-office — three-dimensional films, of all things. This latest wide-eyed wonder (of a temporary nature, of course) is the effusion of Natural Vision Corp. which, employing age-old technical knicknacks, comparatively speaking, promises to open up the road to the Promised Land. As reported, Natural Vision goes like this; The only special equipment necessary to photograph a picture in the Natural Vision system includes a housing which holds two standard cameras facing each other. They receive their images from two mirrors mounted between their lenses in a V and separated by the normal distance between tne human eyes. The mirrors can be adjusted to angle so that the point of optical convergence will correspond to any focal point at which the cameras are set. Each camera takes a complete negative which may be used to produce standard two-dimensional prints for normal exhibition anywhere. Special Viewing Aids The three-dimensional effect require the use of two prints, one from each negative, two projectors simultaneously, and polarized spectacles for audiences. Transparent gelatins of opposite polarization immediately in front of each projector polarize the beams, which are adjusted to proper convergence on the screen and the viewer equipped with corresponding glasses sees one image with one eye and the other image with the other eye. Consequently, he experiences normal depth perception. The system will work either in color or black-and-white. Disadvantages of System Its disadvantages are several. For continuous screening without interruption for rewinding, a theater must use four projectors instead of the standard two. The system will work only on a metallic-surfaced screen, and many theaters are equipped with porous screens, replacement of which would cost about $200. And, finally, the exhibitor must buy spectacles for his patrons at a cost of five to ten cents a pair, and the patrons must be persuaded to wear them. Nevertheless, says Natural Vision, the obstacles are by no means insuperable in big, first-run theaters, which normally have three projectors anyway. In situations where innovation is impractical, hopefully explains Natural Vision, a single print can be used to show the picture in the regular two-dimensional form. Readers of IP will recognize in the foregoing much that is oldhat technologically, and this impression will be strengthened after a reading of the adjacent exposition by J. A. Norling. 14 INTERNATIONAL PROJECTIONIST August 1951