Eidophor

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An Eidophor was a television projector used to create theater-sized images. The name Eidophor is derived from the Greek words ‘eido’ and ‘phor’ meaning image bearer. Its basic technology was the use of electrostatic charges to deform an oil surface. Pictures of the early projector can be seen here.

The idea for the original Eidophor was conceived in 1939 in Zurich by Dr Fritz Fischer and the Swiss Federal Institute of Technology with the first prototype being unveiled in 1943. A patent was granted by the United States Patent and Trademark Office (patent no. 2,391,451) to Friederich Ernst Fischer for the 'Process and appliance for projecting television pictures' on 25th December, 1945. An original August 1952 magazine article in the Radio and Television News [1] credits the development of the Eidophor to Dr Edgar Gretener. It was not until around the time of this article that Gretener took a lead in commercialising the Eidophor, following Fischer’s death in 1947.

Eidophors used an optical system somewhat similar to a conventional movie projector but substituted a slowly-rotating mirrored disk or dish for the film. The disk was covered with a thick transparent oil and through the use of a scanned electron beam, electrostatic charges could be deposited onto the oil, causing the surface of the oil to deform. Light was shone on the disc via a striped mirror consisting of strips of reflective material alternated with transparent non-reflective areas. Areas of the oil unaffected by the electron beam would allow the light to be reflected directly back to the mirror and towards the light source, whereas light passing through deformed areas would be displaced and would pass through the adjacent transparent areas and onwards through the projection system. As the disk rotated, a doctor blade discharged and smoothed the ripples in the oil, readying it for re-use on another television frame.

The Eidophor was a large and cumbersome device and not commonly used until there was a need for good quality large screen projection. This opportunity arose as part of the Nasa space programme where the technology was deployed in mission control.

Eidophor projectors in use at Nasa’s Mission Operation Control Room

Simple Eidophors produced black-and-white images. Later units used a CBS-style sequential color wheel, to produce red, green, and blue fields. The last models produced used separate red, green, and blue units in a single case. The Eidophor was eighty times brighter than CRT projectors of the time. The last Eidophors were able to project colour images of up to 18 metres in width. Advances in projection television technology in the 1990’s brought about the end of the Eidophor. The new devices were smaller and cheaper and produced comparable results. Current technologies include the Liquid Crystal Display (LCD) and Digital Light Processing (DLP) projectors, both of which produce superior results from easily portable devices.