The Iconoscope was the name given to an early television camera tube in which a beam of high-velocity electrons scans a photoemissive mosaic. A research group at RCA headed by Vladimir Zworykin introduced the Iconoscope in 1934 [ [http://www.google.com/patents?id=ugN-AAAAEBAJ Method of and apparatus for producing images of objects] , U.S. patent #2,021,907, filed November 13, 1931, patent issued 1935.] , after visiting Philo Farnsworth's lab and examining in 1930 how the world's first electronic television camera had been designed, for a potential licensing deal for his new employer, RCA. The Iconoscope was a leading camera tube used for broadcasting in the United States from 1936 until 1946.


Images were projected onto a photosensitive plate, which broke up the image into thousands of picture elements now known as "pixels." A scanning electron beam traversed the face of the plate, "charging" all the pixels. Each pixel retained an electrical charge proportional to the light energy initially projected onto it which was fed to the output of the camera. In this way, a visual image was converted to an electrical signal.

The key aspect of the Iconoscope was that the image-sensitive target integrated, or collected the charge developed by the light hitting it between readout scans.

Other early electronic tubes

Zworykin had previously filed a patent an electronic camera for Westinghouse in 1923 that used a two-sided target. The image fell on the photosensitive front of the plate, while the cathode ray beam swept the rear of the plate. But after years of improvements, the image quality was still mediocre, with numerous technical problems, and it never left the laboratory stage. The patent was never granted.

The first all-electronic camera tube to be demonstrated and patented was the Image Dissector by Philo Farnsworth in 1927 (patent issued in 1930). RCA believed Farnsworth's patent was written so broadly as to exclude any other electronic image formation system, including the Iconoscope, and filed a patent interference suit, asserting that Zworykin's 1923 design preceded Farnsworth's Image Dissector. But priority of invention was awarded in 1935 to Farnsworth.

One drawback of Farnsworth's Image Dissector was that since it was not a storage tube, it required even more bright, hot lights in the television studio than the Iconoscope. The Zworykin Iconoscope of 1931 required less lighting than Farnsworth's image dissector, was easier to manufacture, and produced a clear image. While the Iconoscope was replaced in the late 1940s with the Image Orthicon tube, many of the basic concepts were retained, such as the use of a photosensitive plate and the scanning electron beam. The word "image" in the name of the Image Orthicon refers to the fact that it utilizes an electron-emission section (like the image dissector) ahead of the photosensitive plate (like the Iconoscope), combining the best aspects of both tubes.

There is some similarity between the Iconoscope and EMI's Emitron camera developed primarily by J. D. McGee, and in theory the EMI team under Isaac Shoenberg may have had access to some RCA research under a patent-sharing agreement. However, when Zworykin published a paper on the Iconoscope in 1933, Shoenberg concluded that EMI was ahead technologically and had little to learn from Zworykin's development, turning down an offer of technical assistance from RCA.

ee also

*Video camera tube

External links

* [http://www.ieee-virtual-museum.org/collection/tech.php?id=2345791&lid=1 Iconoscope history]
* [http://www2.fht-esslingen.de/telehistory/ikonoskp.html Iconoscope pictures]


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