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Large Screen Colour TV

Wireless World, June, 1960.
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Eidophor projectors in process of manufacture.

The Eidophor system for projecting television pictures on large screens has now been adapted for colour television, and recently we saw a demonstration of its capabilities for closed-circuit work at Belle Vue, Manchester, given by CIBA Clayton Ltd., the dye manufacturers. In the Eidophor projector (made in Switzerland by Gretag AG, with the backing of CIBA, the Swiss chemical combine) light from a powerful xenon arc lamp is modulated by means of an oil film which is electrostatically deformed in the pattern of the television picture by a scanning electron beam. The deformations in the film actually modulate the light by refraction - by altering the angle at which the light is reflected from a concave mirror behind the oil film. An optical interception system (Schlieren system) in the path of the reflected light then causes the beam-angle variations to produce corresponding beam-intensity variations in the light emerging from the projector.

Adaptation to colour television has been achieved by using the frame-sequential system with synchronized rotating colour filters in front of the camera and projector. For the demonstration three image orthicon cameras were set up at CIBA Claytons Technical Service Laboratories in Manchester and the signals were transmitted 1½ miles by microwave link to Belle Vue for projection on a screen measuring 10ft x 7ft. The cameras were American types and the 525-line standard was used.

The advantage of the Eidophor system over CRT projection systems is, of course, the greater brightness obtained by modulating a normal light source. This was very evident at the demonstration, although the pictures suffered a certain amount of spasmodic flicker. Definition was excellent for a large screen (there are no image registration problems with the frame sequential system) and the colour rendering was as good as the quality of the rotating colour filters.

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