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Aspheres in the Home

“The picture is too small!” Pre-war television had its share of critics. RCA scientists I. G. Maloff and D. W. Epstein developed an interesting optical system to help address the image-size problem in 1940. It was based on the earlier work of G. A. H. Kellner and B. W. Schmidt.

A typical pre-war television display measured about 7″x10″ and had a viewing distance of about 30″. The experimental RCA “Large-Screen Receiver” had a 16″x21″ display and extended the viewing distance to ~10′. Later versions extended both display size and viewing distance.

The optical system depicted below was the key ingredient. Notice the design progression in the RCA technical marketing literature, starting with film projection and ending with a corrected reflecting system.

From Radio News, September 1947: “The RCA reflective optical system for television projection is a development evolved from the reflection principles of optical apparatus devised by (G. A. H.) Kellner and by (B. W.) Schmidt. Forty years ago, an American lens designer, Kellner, patented a reflective optical system for light transmission by searchlight or by the headlights of an automobile (Bausch & Lomb Optical Company, Rochester, NY). Twenty-five years later or fifteen years ago, a German optician, Schmidt, invented a camera with a reflective optical system which provided a large aperture ratio and a wide field of view, and was widely used in astronomy.”

A significant innovation in these early projection televisions was the implementation of low-cost optical manufacturing techniques, particularly the large molded asphere.

As an aside to the home systems, by 1947, RCA had reported on projection systems, which placed 70kV on the picture tube and used 30″ diameter reflectors and 22.5″ diameter glass aspheres. The projection screen was 15′ x 20′ and the application was theater television.

There is more to say about aspheres-in-the-home. And for further reading, see:

G. A. H. Kellner, “Projecting Lamp,” US Patent 969,785, September 13, 1910.

A. J. Timoney, “Motion Picture Projection Device,” US Patent 1,753,222, April 8, 1930.

C. H. Fetter, “Photgraphic Projection Device,” US Patent 2,216,512, October 1, 1940.

V. K. Zworykin, “Color Television,” US Patent 2,566,713, September 4, 1951.

J. H. O. Harries et al, “Facetted Correction Lens for Minimizing Keystoning of Off-Axis Projectors,” US Patent 2,999,126, September 5, 1961.