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1953-54 Theatre Catalog, 11th Edition, Page 401 (363)

1953-54 Theatre Catalog, 11th Edition
1953-54 Theatre Catalog
1953-54 Theatre Catalog, 11th Edition, Page 401
Page 401

1953-54 Theatre Catalog, 11th Edition, Page 401



999 WEJT 56771.57?



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THE OPERATION OF THE EIDOPHOR SYSTEM is illustrated in this simplified artist's conception.

In the Eidophor system the light from the arc passes through auxiliary lenses to a plane mirror arranged in parallel bars and set at about 45 degrees to the light beam direction, which reflect half the light downward. Half because the widths of the mirror bars and of the spaces between them are substantially equal. So half the light is lost, just as half the light is lost by shutter blades in the standard motion picture projector. The light that travels downward strikes the Eidophor liquid film and the reflecting mirror surface on which the liquid is carried.

This mirror rehects the light straight back along the same path, provided there is no picture, or distortion on the Eidophor liquid surface. When there is no picture, the reflected light strikes the tilted mirror bars, and is again reflected back to the lamp house, not to the screen. Hence, there is no light on the screen when there is no picture on the Eidophor liquid. However, when a picture is formed on the Eidophor liquid, the optical properties of the liquid layer are changed, and the light reflected by the Eidophor mirror is bent aside or deflected, enabling it to pass through the slots between the tilted bars. The picture forming light passes through the objective lens and then strikes a final mirror which directs it to the screen.

Since the amount of deflection of the light from each point-by-point area of the Eidophor picture depends on the amount of deformation of the liquid at that picture point, and since each picture is scanned by the electron beam many times a second, a complete picture reaches the screen.

The pictures seem to have action of course, just as do moving pictures, or home television pictures, because the


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component images follow each other in such rapid succession that the human eye cannot see the pictures separately.

Color Problem

A final consideration is the color problem. Motion pictures can be made in color if three separate films are usedone color in a manner to produce on the screen red light yielding a stimulus equivalent to the red stimulus received by the eye when it views the scene; one colored blue in a similar way; and one similarly colored green. If these three partial color pictures are projected together, a complete picture in natural color will result.

Now these separate color records may be projected at the same instant, that is simultaneously; but they could equally well be projected one after the other at a sufficiently rapid rate so that the eye does not see the colored images as separate and distinct single color pictures.

This latter system is roughly the field of sequential method of CBS color television; the same basic technique which is used with the Eidophor system. The theatre television standards are considerably improved over home television. A small wheel composed of red, blue, and green segments is inserted in the beam of light at the arc lamp of the projector, and is rotated so that the red, blue, and green segments are placed in position in the beam at the instant that the television signal contains picture information of the corresponding color.

The Eidophor process has a number of advantages beyond those already mentioned, which are of interest mainly from a technical point of view. Among those the ustorage time'l of the picture on the Eidophor liquid can be controlled for greatest efficiency; the system is not limited to field sequential color methods asimultaneous projection of color field is also possible. However, it is believed that the quality of the results, from the

simple and straight-forward field sequential method of producing large Screen TV pictures in color, warrants its immediate use.


The Eidophor projector makes use of an arc-light source for the illumination of the large screen picture. The brightness, therefore, as in film projection, depends largely on the intensity of this light source. This fact, and the relatively high efficiency of the system, enables the production of very high screen illumination. Light rays from the arc source are passed through an optical lens and onto a Schlieren optical plane placed at 45 degrees to the light source path. The Schlieren optical system consists of a series of front silvered mirror strips positioned in a plane and equally spaced with their separation equal to their width, so that half the light passes through to an absorptive surface. The remaining 50 per cent is reflected at 90 degrees and uniformly illuminates an area, approximately seven and a half by 10 centimeters, on a concave mirror surface. The concave surface of the mirror casting has a thin coating of special oil, the Eidophor liquid. A very slow rotation of the mirror, in conjunction with a smoothing plate in contact with the liquid, is used to maintain a smooth liquid surface which otherwise would be subjected to a gradual physical deformation as a result of continued scanning by the electron beam. The casting, and hence the liquid coating, is maintained at a controlled temperature in order to achieve the proper time constant characteristics for video signal response and

scanning rates.

Electron Beam

The area of the liquid, which is exposed to the illumination of the arc source, is also scanned by an electron beam carrying the picture information. The orientation of the scanning lines is at right angles to the Schlieren strips. The electron gun which generates the beam is conventional in that magnetic focusing and deflection for faster scanning are employed, however, a bombarded cathode is used. This system is unique in its use of added electrostatic deflection plates to which the picture signal is applied. These plates are so positioned as to superimpose small deHections parallel to the direction of the horizontal scanning lines. A 50 megacycle carrier, which is amplitude modulated by the picture signal video, is applied to these electrostatic deflection plates. This produces a variation of density of charge deposited along each scanning line on the Eidophor liquid.

Under the influence of electrostatic forces from the charges deposited by the scanning beam, the surface of the oil is deformed or dimpled along the Scanning lines at a 50 megacycle sine wave rate. The depth of these dimples during each picture element is proportional to the amplitude of this carrier, which amplitude is determined by the video signal.

If there are no deformations on the liquid surface it is so shaped as to image the light from each of the silvered strips of the Schlieren mirror back on itself and then back to the arc source. Deformations
1953-54 Theatre Catalog, 11th Edition, Page 401