> > > >

1953-54 Theatre Catalog, 11th Edition, Page 259 (223)

1953-54 Theatre Catalog, 11th Edition
1953-54 Theatre Catalog
1953-54 Theatre Catalog, 11th Edition, Page 259
Page 259

1953-54 Theatre Catalog, 11th Edition, Page 259

proves to be an economic disadvantage of the beam splitter method. There is a corresponding light loss in projection, and here the loss is even more significant. Take the loss inherent in the beam splitter, add that to the loss in polarization and you find that youfre getting about one-twelfth the light that you had when you projected the full frame in the conventional way. Another disadvantage of the ordinary beam-splitter is the picture proportions it givesea narrow and tall picture, certainly inappropriate for stereoscopic representation which is so well suited for panoramic Views.

Another proposed device has dual lenses producing pictures side by side. There is no light loss in the camera, since two lenses are used and the window for each picture is quite sharp. However. there is considerable loss in projection if the attachment is used on a projector not provided With a Special condenser system. If the standard pro light period of the same, then a long dark period consuming 62.5 per cent for pull-down and eclipse to permit the other eye to see its image. If standard soundfilm speed of 24 frames a second is used, the resulting hicker is very annoying. Stepping up the projection to 48 frames a second increases flicker frequency twice, but it still is noticeable. There is a physiological effect that is likely to become disagreeably apparent *usually headache or nausea-after a few minutes of viewing pictures projected in this way. A complete period of darkness for one eye, while light reaches the other, will probably always result in visual fatigue, if not in nausea, no matter how high, within workable limits, the flicker frequency is brought.

Flicker of low frequency calls for traction on the control muscles of the irises when bright light enters one or both eyes. The rapid occurrence of the transmission of stimuli, first from one eye, then from the other, and the motor

DIAGRAM OF THE "ANAMORPHOSEH" principle applied to motion picture photography is seen below.




comancrso IMAGE cm FILM

portions are retained, each image is less than one-fourth the area of the full frame.

Another method which has been proprosed for simultaneous projection, is the arrangement of images with one member above the other. Special p-rojectors would be required.

Sequenfial Frame Proiecfion"Eclipse" System

From time to time, the alternate projection of the members of a stereo pair has also been proposed. In this system, the right eye image, for instance, is projected first, then the shutter interrupts the light beam while the film moves down to position the left eye image. Thus there are periods of flicker that occur at different times for each eye. If we break this sequence of events down, we find that the first light period has a value of 12.5 per cent of the complete picture cycle. The flicker blade on the projector shutter (considering a twobladed shutter) gives a dark period last ing 12.5 per cent to be followed by :1



*commcrso IMAGES

messages from the brain to the muscles, delivered in rapid sequence, probably accounts, in part, for the visual discomfort experienced by most people when viewing ffeclipse" stereo movies.

Perception of flicker depends upon the flicker frequency. The more intense the light, the higher the frequency must go before flicker fusion is attained. Also, the larger the angular field over which flicker is distributed, the greater the consciousness of flicker. Hence the dimmer the picture and the smaller it is, the lower becomes the flicker fusion frequency.

There are two ways to project and view eclipse stereograms. One is by using rotating or vibrating shutter devices held up in front of the eyes. These are synchronized electrically with the projector. The other method is to employ a rotating polarizer in front of the projector lens and polarizing spectacles for the viewer. In one position the polarizer delivers light through the left spectacle filter, in the other through the right filter.

Alternate frame, or eclipSe, projection should have at least twice the number

INTERLOCKED 16mm cameras for 3-D photography.

of frames required for conventional films. That means doubling the length and providing for faster projection speed. If the alternate frames are photographed alternately, there is a very objectionable fringing in pictures of moving objects. This is a cause of eyestrain, especially in a picture where the action seen by one eye is in quite a different stage of progress than the action seen by the other. Difficulty in fusion invariably results. This combination of disturbing effects caused by flickers out of phase between the eyes and by fusion trouble, limits the appreciation of the eclipse method.

Complete visual comfort can be at tained in stereo movies only if the two images are projected simultaneously, if they are rock-steady, if they are of equal brightness, if they are of equal contrast, if they are properly aligned vertically and horizontally, if far distant points are not separated too far in one image from that of the other, and if they are of exactly the same size.

Improved Single Film Mefhods

Several inventions by the author eliminate the draw back of the single-film dualnimage arrangement, namely the unequal distribution of light. These methods

16mm PROJECTORS interlocked for 3-D projection.
1953-54 Theatre Catalog, 11th Edition, Page 259