Color Mechanical Television
Mechanical television returned to the United States as a method of painting colors over a monochrome CRT. The CBS color television system of Peter Goldmark used such technology in 1940. John Baird's 1928 color television experiments had inspired Goldmark's more advanced field-sequential color system. In Goldmark's system, stations transmit color saturation values electronically. Yet mechanical methods also come into play. At the transmitting camera, a mechanical disc filters hues (colors) from reflected studio lighting. At the receiver, a synchronized disc paints the same hues over the CRT. As the viewer watches pictures through the color disc, the pictures appear in full color.
Of course, simultaneous color systems superseded the CBS-Goldmark system. Yet mechanical color methods continued to find uses. Early color sets were very expensive, over $1,000 in the money of the time. Inexpensive adapters allowed owners of black-and-white, NTSC television sets to receive color telecasts. The most prominent of these adapters is Col-R-Tel, a 1955 NTSC to field-sequential converter. This system operates at NTSC scanning rates, but uses a disc like the obsolete CBS system had. The disc converts the black-and-white set to a field-sequential set. Meanwhile, Col-R-Tel electronics recover NTSC color signals and sequence them for disc reproduction. The electronics also synchronize the disc to the NTSC system. In Col-R-Tel, the electronics provide the saturation values (chroma). These electronics cause chroma values to superimpose over brightness (luminance)changes of the picture. The disc paints the hues (color) over the picture.
A few years after Col-R-Tel, Apollo moon missions also adopted field-sequential techniques. The lunar color cameras all had color wheels. These Westinghouse and later RCA cameras sent field-sequential color television pictures to earth. The earth receiving stations included mechanical equipment that converted these pictures to standard television formats.
Today, some Digital Light Processing (DLP) projectors still use color filter wheels.
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