American cinematographer (Nov 1921-Jan 1922)

January 1, 1922 THE AMERICAN CINEMATOGRAPHER 13 Stereoscopy and Its Application to Cinematography (Continued from Page 51 the eye to clearly discern the blue image, and the blue glass obliterates the blue image, but allows the eye to clearly discern the red image. Therefore, if the right eye image is printed in red, a blue glass should be placed over the right eye; and if the left eye image is blue, a red glass should be placed over the left eye. The above principle was utilized by J. Ch. D'Almeida, also of France, for optical lantern projection. He employed two lanterns, and placed in each stage an element of a stereoscopic pair of lantern slides. Over each lens he placed respectively a red and green screen. The two lanterns were adjusted to bring the slide into approximate register. The observer simply had to wear a pair of spectacles provided with red and green glasses to see. the picture in stereoscopic relief. It will be noticed that du Hauron employed the subtractive method, while D'Almeida utilized the additive method for projection. The subtractive method is much preferable for projection, inasmuch as each element can be toned in complementary colors and bound together as one slide. This necessitates only a single lantern for projection, and the loss of light involved is very much less than by additive projection. 2. The Eclipse System. — This is also an invention of D'Almeida. Two optical lanterns were placed side by side and each stage contained a stereo element. In front of the lenses a revolving shutter was arranged in such a manner as to uncover each lense alternately. A mechanically operated shutter was also arranged in front of the eyes of each observer, operating in synchronism with the shutter of the lanterns. When the right eye element was being projected the right eye was uncovered, and when the left eye element was being projected the left eye was uncovered. As the shutters rotated at a speed of 24 revolutions per second, perfect stereoscopic relief resulted by virtue of persistence of vision. Jenkins of Washington patented a similar method, but operated the observing shatters electrically by means of solenoids operated through a commutator on the projector. 3. The Polarized Light System. — In the early nineties John Anderton of Birmingham. England, invented the above system. Basing his idea on the principle that if a beam of light from an optical lantern is passed through a polorizing medium such as a Nicol prism ( Polarizer ) of Iceland Spar, the beam will continue uninterruptedly to the screeii. If this polarized beam be observed through another Nicol prism (analyzer) there will be no change at the screen if the analyzer is arranged n the same plane as the polarizer. The beam will be totally extinguished, however, if the analyser is arranged at right angles to the polarizer. Anderton employed two optical lanterns. Between the combinations of each lens he arranged polarizes composed of bundles of thin glass plates at right angles to each other. For analysers he constructed small binoculars fitted with bundles of thin glass plates also arranged at right angles to each other. Right and left elements of a stereoscopic pair of transparencies were placed in each lantern and projected in approximate register on the screen, and observed through the analyzers. The stereoscopic principle being fulfilled as in the former cases perfect relief has been the result. With certain necessary modifications, the three systems discussed above, are applicable to cinematography. For instance, by modifying the camera to take alternate right and left eye impressions on a single strip of standard negative film, and making a positive print from such a negative, such a print is admirably suitable for projection by the three named methods. For the Complimentary Color System, all that is required is to either fit a revolving shutter to the projector provided with red and green sectors and rotating at half the speed of the regular shutter, or to tint each alternate picture red and the remaining pictures green (additive method). Or to tone each alternate picture of the . same color (subtractive method). Viewing the result with complimentary glasses. By the eclipse system, each observer may be provided with an electrically operated (solenoid) viewing device, running in synchronism with the projector by means of a commutator, and the necessary electrical connections to each viewing device. By the Polarized Light System, the projected beam may pass through a tube of suitable liquid, around which is wound a number of turns of insulated copper wire, and an intermittent current passed through the coil and controlled by a commutator on the projector. Each successive picture through the action of the current .will be plane polarized to the next. If the resultant jumbled image be viewed by a pair of analyzers the stereoscopic relief will result. Now, as to the merits of each method. The Polarized Light System is impractical on account of the Light cost of the viewing devices; and the loss of light involved by this method is considerable. The Eclipse System as regards results is the best; but the viewing devices are costly, and are liable to damage by careless handling. Natural color pictures are well adapted to this method. The Complimentary Color System gives more promise of success. The viewing devices are inexpensive. Additive projection by this method is a simple matter when a rotating color wheel is fitted to the projector. The preparation of the positives by tinting and toning offer a much more serious problem; herein lies the greatest difficulty. For the use of schools and scientific institutions the Complimentary Color System offers wonderful opportunities; and all efforts should be made to introduce this beautiful method of presenting motion pictures to small audiences. From the standpoint of the theatre all the above methods must prove impractical. It is not possible to efficiently control such large audiences. From the foregoing discussion, we will all unanimously agree that what is needed is a stereoscopic motion picture that may be termed direct, i. e., one that does not render necessary the use of intermediate optical means for viewing the result. I will now mention a few methods that have been tried by a number of experimenters entirely ignorant of the fundamental laws of stereoscopy, and the disastrous results obtained by such methods. Most of these methods are based on taking right and left images in alternate order on the film strip; each experimenter employing a separation to conform to his individual desire. Separation of viewpoints vary from half an inch to nine inches. Various optical systems have been evolved to obtain the above results; a few conform to good optical principles, while the majority are impossible. The results obtained by these methods may produce stereoscopic effects, if viewed by intermediate optical means, in varying degrees of relief; but these experimenters all cherish the hope, that the resultant positives if projected on the screen should bloom out in beautiful stereoscopic relief. They consider intermediate optical means superfluous. Others have tried using one lens with a large relative aperture; a piece of black cardboard pierced with two small apertures diametrically opposite to each other is introduced in front of the lens (Concluded on Page 14) I?' 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