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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]

Contents

Operation

Within the iconoscope an image was projected onto a plate containing a mosaic of photosensitive granules. An insulating layer separated them from a shared common plate. Therefore, each granule constituted a tiny capacitor that accumulated and stored an electrical charge proportional to the light striking it. A scanning electron beam periodically swept across the plate, discharging the capacitors and providing the electrical output of the tube.[2][3] In the 1934 version the electron beam scanned the granules instead of the capacitor plate.[1]

The key aspect of the iconoscope was that, together with the camera build by Philo Farnsworth, and the one by Kálmán Tihanyi, the iconoscope with its electronic scanning mechanism was a step ahead of the mechanical scanning mechanism used in the Nipkow disk.

As compared to the other electronic designs, the light-sensitive target accumulated and stored photoelectric charges between each discharge scanning cycle, thus greatly increasing its electrical output relative to image intensity.

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]

Hungarian engineer Kálmán Tihanyi filed a patent application for the first all-electronic television system, the "Radioskop", on March 20, 1926. His design included design of a camera tube employing the principle of "charge storage" — the accumulation and storage of electrical charges ("photoelectrons") throughout each scanning cycle, greatly increasing the electrical output of the tube.[6][7] Although his 1926 application was never acted upon,[8] he added improvements to the design in applications filed in Hungary and Germany in 1928,[8][9], and in the U.S. in 1929 and 1935. The U.S. patent for his camera tube was granted and assigned to RCA in 1939.[10] Tihanyi's "charge storage" principle was incorporated into RCA's design of the Iconoscope.[11]

The first practical all-electronic camera tube was the Image Dissector, demonstrated by American inventor Philo Farnsworth in 1927[12] and patented in 1930.[13] RCA asserted that 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 to Farnsworth in 1935.

A major drawback of the Image Dissector was that since it was not a storage tube, it required much more light to be effective. The Iconoscope not only required less light, but was easier to manufacture, and produced a clearer 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.

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.

Related

  • Video camera tube

External links

References

  1. ^ a b Vladimir Zworykin (filed 1931, patented 1935). "Method of and Apparatus for Producing Images of Objects". Patent No. 2,021,907. United States Patent Office. http://www.google.com/patents?id=ugN-AAAAEBAJ. Retrieved 2009-05-21. 
  2. ^ a b c Vladimir Zworykin (filed 1923, patented 1938). "Television System". Patent No. 2,141,059,. United States Patent Office. http://www.google.com/patents?id=bdYBAAAAEBAJ. Retrieved 2009-05-21. 
  3. ^ a b c Vladimir Zworykin (filed 1925, patented 1928). "Television System". Patent No. 1,691,324,. United States Patent Office. http://www.google.com/patents/about?id=mZ9KAAAAEBAJ. Retrieved 2009-07-28. 
  4. ^ a b Albert Abramson, The History of Television, 1942 to 2000, McFarland, 2003, p. 18. ISBN 0786412208.
  5. ^ Christine Heimprecht. "Fernsehkamera – Dr. Walter Bruch und die Olympiakanone" (in German). Zukunftsinitiative Rheinland-Pfalz (ZIRP) e.V.. http://www.erfinderland-rlp.de/Erfindungen/Fernsehkamera.htm. Retrieved 2009-05-21. "Picture of the iconoscope camera used at the Olympic Games Berlin, 1936" 
  6. ^ "Kálmán Tihanyi's 1926 Patent Application 'Radioskop'", Memory of the World, United Nations Educational, Scientific and Cultural Organization (UNESCO), 2005, retrieved 2009-01-27.
  7. ^ Glass, Katalin Tihanyi, "The Iconoscope: Kalman Tihanyi and the Development of Modern Television", Review of Technics, National Museum for Science and Technology, Budapest, 2000-06-23, retrieved 2009-07-29.
  8. ^ a b Gecsényi, Lajos , Memory of the World nomination form: Hungary - Kalman Tihanyi’s 1926 Patent Application “Radioskop”, United Nations Educational, Scientific and Cultural Organization (UNESCO), 2005, retrieved 2009-07-29.
  9. ^ "Kálmán Tihanyi (1897-1947)", IEC Techline, International Electrotechnical Commission (IEC), 2009-07-15.
  10. ^ Television Apparatus, United States Patent Office, Patent No. 2,158,259, May 16, 1939.
  11. ^ Doug Elliot, "The Beginning of Television", History Magazine, Vol. 7 No. 3, March 2006, Moorshead Magazines Ltd.
  12. ^ "Philo Taylor Farnsworth (1906-1971)", The Virtual Museum of the City of San Francisco, retrieved 2009-07-29.
  13. ^ Philo T. Farnsworth (filed 1927, patented 1930). "Television System". Patent No. 1,773,980,. United States Patent Office. http://www.google.com/patents/about?id=HRd5AAAAEBAJ. Retrieved 2009-07-28.