iconoscope

Zworykin's patent diagram of a UV-microscope 1931.^[1] The apparatus is similar to the iconoscope. The image entered through the series of lenses at upper right, and hit the photoelectric cells on the image plate at left. The cathode ray at the right swept the image plate, charging it, and the photoelectric cells emitted an electric charge in variance with the amount of light hitting them. The resulting image signal was carried out the left side of the tube and amplified.

The Iconoscope (from the Greek: εἰκών "image" and σκοπεῖν "to look, to see") was the name given to an early television camera tube in which a beam of high-velocity electrons scans a photoemissive mosaic. Some of the principles of this apparatus were described when Vladimir Zworykin filed two patents for a Television system in 1923 and 1925.^[2][3]

A research group at RCA headed by Vladimir Zworykin introduced the Iconoscope in 1934.^[4] The German company Telefunken bought the rights from RCA and built the Iconoscope camera^[5] used for the historical TV transmission at the Olympic Games in Berlin 1936.

The Iconoscope was the leading camera tube used for broadcasting in the United States from 1936 until 1946.^[4]

Operation

Within the iconoscope, an image was projected onto a plate containing a mosaic of photosensitive granules separated from a common plate, each constituting a tiny capacitor that accumulated and stored electrical charge in response to the light striking it. An electron beam periodically swept across the plate, effectively scanning the stored image and discharging each capacitor in turn such that the electrical output from each capacitor was proportional to the average intensity of the light striking it between each discharge event.^[2][3][6] The accumulation and storage of photoelectric charges during each scanning cycle greatly increased the electrical output of the iconoscope relative to non-storage type image scanning devices.^{[citation needed]} In the 1934 version, the electron beam scanned the granules instead of the capacitor plate.^[1]

Other early electronic tubes

Zworykin had previously filed two patent applications for an electronic camera that used a two-sided target for Westinghouse in 1923 and 1925. 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 development there were still numerous technical problems and the image quality remained poor. Although it never left the laboratory stage, the patents were granted in 1938 and 1928, respectively.^[2][3]

In 1926, Kálmán Tihanyi filed a patent application in Hungary for an all-electronic television system dubbed "Radioskop" that included a camera tube employing "charge storage" — the accumulation and storage of electrical charges ("photoelectrons") throughout each scanning cycle — thus greatly increasing the electrical output of the tube.^[7][8] Although his 1926 application was never acted upon,^[9] he added improvements to the design in applications filed in Hungary and Germany in 1928,^[9][10] and in the U.S. in 1929. RCA acquired the U.S. rights to Tihanyi's patents, and "charge storage" was incorporated into the design of the Iconoscope, although the U.S. patent for Tihanyi's camera tube was not granted until 1939.^[11][12]

The first practical all-electronic camera tube was the Image Dissector, successfully demonstrated in 1927 by American inventor Philo Farnsworth,^[13] who had applied for a patent for the device in January 1927 which would be issued in 1930.^[14] A major limitation of the original Image Dissector was that, because it lacked charge storage, it required a great deal of light to be effective. (This and other limitations were addressed in a 1933 patent application for a redesigned Image Dissector employing charge storage and cathode-ray scanning.^[15]) The Iconoscope not only required less light, but was easier to manufacture and produced a clearer image.^{[citation needed]} While the Iconoscope was replaced in the late 1940s with the Image Orthicon, many of the basic concepts were retained, such as the use of a photosensitive plate and the scanning electron beam.^{[citation needed]}

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.^{[citation needed]}

See also

• Image Dissector
• Video camera tube

External links

• Iconoscope history
• Iconoscope pictures

References