Iconoscope
Encyclopedia
The Iconoscope was the name given to an early television camera tube in which a beam of high-velocity electron
s scans a mosaic
of photoemissive isolated granules. Some of the principles of this apparatus were described when Vladimir Zworykin
filed two patents for a Television system in 1923 and 1925.
A research group at RCA
headed by Vladimir Zworykin
presented the iconoscope to the general public in a press conference in June 1933, and two detailed technical papers were published in September and October of the same year. The German company Telefunken
bought the rights from RCA and built the Iconoscope camera 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, when it was replaced by the image orthicon tube.
, 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. 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. In the 1931 version, the electron beam scanned the granules; while in the 1925 version, the electron beam scanned the back of the image plate.
, and Zworykin was asked to work on something useful.
A patent for a television system was also filed by Zworykin in 1923, but this file is not a reliable bibliographic source because extensive revisions were done before a patent was issued fifteen years later and the file itself was divided into two patents in 1931. In 1926, the Hungarian engineer Kálmán Tihanyi
explained in detail that the principle of "storing" electrical charges in proportion to the amount of light received throughout each scanning cycle results in a much more sensitive video camera tube. Although his 1926 application was never acted upon, two year later, in 1928, Tihanyi applied for a patent for a refined "Television Apparatus" that is essentially an iconoscope.
The first practical iconoscope was constructed in 1931 by Sanford Essig, when he accidentally left one silvered mica sheet in the oven too long. Upon examination with a microscope, he noticed that the silver layer had broken up into a myriad of tiny isolated silver globules. He also noticed that: the tiny dimension of the silver droplets would enhance the image resolution of the iconoscope by a quantum leap. As head of television development at Radio Corporation of America (RCA), Zworykin submitted a patent application in November 1931, and it was issued in 1935. Nevertheless, Zworykin's team was not the only engineering group working on devices that use a charge stage plate. In 1932, Tedham and McGee under the supervision of Isaac Shoenberg
applied for a patent for a new device they dubbed "the emitron", a 405-line broadcasting service employing the emitron began at studios in Alexandra Palace
in 1936, and a patent was issued in the USA in 1937. One year latter, in 1933, Philo Farnsworth
also applied for a patent for a device that use a charge storage plate and a low-velocity electron scanning beam, a patent was issued in 1937, but Farnsworth did not know that the low-velocity scanning beam must land perpendicular to the target and he never actually built such a tube.
The iconoscope was presented to the general public in a press conference in June 1933, and two detailed technical papers were published in September and October of the same year. Unlike the Farnsworth image dissector, the Zworykin iconoscope was much more sensitive, useful with an illumination on the target between 4ft-c
(43lx
) and 20ft-c
(215lx
). It was also easier to manufacture and produced a very clear image. The iconoscope was the primary camera tube used in American broadcasting from 1936 until 1946, when it was replaced by the image orthicon tube.
On the other side of the atlantic ocean, the British team formed by engineers Lubszynski, Rodda, and MacGee developed the super-emitron (or super-iconoscope) in 1934, this new device is between ten and fifteen times more sensitive than the original emitron and iconoscope, and it was used for a public broadcasting by the BBC
, for the first time, on Armistice Day 1937.
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s scans a mosaic
Mosaic
Mosaic is the art of creating images with an assemblage of small pieces of colored glass, stone, or other materials. It may be a technique of decorative art, an aspect of interior decoration, or of cultural and spiritual significance as in a cathedral...
of photoemissive isolated granules. Some of the principles of this apparatus were described when Vladimir Zworykin
Vladimir Zworykin
Vladimir Kozmich Zworykin was a Russian-American inventor, engineer, and pioneer of television technology. Zworykin invented a television transmitting and receiving system employing cathode ray tubes...
filed two patents for a Television system in 1923 and 1925.
A research group at RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
headed by Vladimir Zworykin
Vladimir Zworykin
Vladimir Kozmich Zworykin was a Russian-American inventor, engineer, and pioneer of television technology. Zworykin invented a television transmitting and receiving system employing cathode ray tubes...
presented the iconoscope to the general public in a press conference in June 1933, and two detailed technical papers were published in September and October of the same year. The German company Telefunken
Telefunken
Telefunken is a German radio and television apparatus company, founded in Berlin in 1903, as a joint venture of Siemens & Halske and the Allgemeine Elektricitäts-Gesellschaft...
bought the rights from RCA and built the Iconoscope camera used for the historical TV transmission at the Olympic Games
Olympic Games
The Olympic Games is a major international event featuring summer and winter sports, in which thousands of athletes participate in a variety of competitions. The Olympic Games have come to be regarded as the world’s foremost sports competition where more than 200 nations participate...
in Berlin 1936.
The Iconoscope was the leading camera tube used for broadcasting in the United States from 1936 until 1946, when it was replaced by the image orthicon tube.
Operation
Within the iconoscope, an image was projected onto a plate containing a mosaic of electrically isolated photosensitive granules separated from a common plate by a thin layer of isolating material, each granule constituting a tiny capacitor with the common plate that accumulated and stored electrical charge in response to the light striking it. Emission of photoelectrons from each granule in proportion to the amount of light received resulted in a charge image being formed on the mosaic. An electron beam was then swept across the image plate from an electron gunElectron gun
An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
, 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. 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. In the 1931 version, the electron beam scanned the granules; while in the 1925 version, the electron beam scanned the back of the image plate.
History
In July 1925, Zworykin submitted a patent application for a "Television System" that includes a charge storage plate constructed of a thin layer of isolating material (aluminum oxide) sandwiched between a screen (300 mesh) and a colloidal deposit of photoelectric material (potassium hydride) consisting of isolated globules. The following description can be read between lines 1 and 9 in page 2: The photoelectric material, such as potassium hydride, is evaporated on the aluminum oxide, or other insulating medium, and treated so as to form a colloidal deposit of potassium hydride consisting of minute globules. Each globule is very active photoelectrically and constitutes, to all intents and purposes, a minute individual photoelectric cell. Its first image was transmitted in late summer of 1925, and a patent was issued in 1928. However the quality of the transmitted image failed to impress to H P Davis, the general manager of WestinghouseWestinghouse Electric (1886)
Westinghouse Electric was an American manufacturing company. It was founded in 1886 as Westinghouse Electric Company and later renamed Westinghouse Electric Corporation by George Westinghouse. The company purchased CBS in 1995 and became CBS Corporation in 1997...
, and Zworykin was asked to work on something useful.
A patent for a television system was also filed by Zworykin in 1923, but this file is not a reliable bibliographic source because extensive revisions were done before a patent was issued fifteen years later and the file itself was divided into two patents in 1931. In 1926, the Hungarian engineer Kálmán Tihanyi
Kálmán Tihanyi
Kálmán Tihanyi , was a Hungarian physicist, electrical engineer and inventor. One of the early pioneers of electronic television, he made significant contributions to the development of cathode ray tubes , which were bought and further developed by the Radio Corporation of America , and German...
explained in detail that the principle of "storing" electrical charges in proportion to the amount of light received throughout each scanning cycle results in a much more sensitive video camera tube. Although his 1926 application was never acted upon, two year later, in 1928, Tihanyi applied for a patent for a refined "Television Apparatus" that is essentially an iconoscope.
The first practical iconoscope was constructed in 1931 by Sanford Essig, when he accidentally left one silvered mica sheet in the oven too long. Upon examination with a microscope, he noticed that the silver layer had broken up into a myriad of tiny isolated silver globules. He also noticed that: the tiny dimension of the silver droplets would enhance the image resolution of the iconoscope by a quantum leap. As head of television development at Radio Corporation of America (RCA), Zworykin submitted a patent application in November 1931, and it was issued in 1935. Nevertheless, Zworykin's team was not the only engineering group working on devices that use a charge stage plate. In 1932, Tedham and McGee under the supervision of Isaac Shoenberg
Isaac Shoenberg
Sir Isaac Shoenberg was an electronic engineer born in Russia who was best known for his role in history of television....
applied for a patent for a new device they dubbed "the emitron", a 405-line broadcasting service employing the emitron began at studios in Alexandra Palace
Alexandra Palace
Alexandra Palace is a building in North London, England. It stands in Alexandra Park, in an area between Hornsey, Muswell Hill and Wood Green...
in 1936, and a patent was issued in the USA in 1937. One year latter, in 1933, Philo Farnsworth
Philo Farnsworth
Philo Taylor Farnsworth was an American inventor and television pioneer. Although he made many contributions that were crucial to the early development of all-electronic television, he is perhaps best known for inventing the first fully functional all-electronic image pickup device , the "image...
also applied for a patent for a device that use a charge storage plate and a low-velocity electron scanning beam, a patent was issued in 1937, but Farnsworth did not know that the low-velocity scanning beam must land perpendicular to the target and he never actually built such a tube.
The iconoscope was presented to the general public in a press conference in June 1933, and two detailed technical papers were published in September and October of the same year. Unlike the Farnsworth image dissector, the Zworykin iconoscope was much more sensitive, useful with an illumination on the target between 4ft-c
Foot-candle
A foot-candle is a non-SI unit of illuminance or light intensity widely used in photography, film, television, conservation lighting, and the lighting industry...
(43lx
Lux
The lux is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is used in photometry as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface...
) and 20ft-c
Foot-candle
A foot-candle is a non-SI unit of illuminance or light intensity widely used in photography, film, television, conservation lighting, and the lighting industry...
(215lx
Lux
The lux is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is used in photometry as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface...
). It was also easier to manufacture and produced a very clear image. The iconoscope was the primary camera tube used in American broadcasting from 1936 until 1946, when it was replaced by the image orthicon tube.
On the other side of the atlantic ocean, the British team formed by engineers Lubszynski, Rodda, and MacGee developed the super-emitron (or super-iconoscope) in 1934, this new device is between ten and fifteen times more sensitive than the original emitron and iconoscope, and it was used for a public broadcasting by the BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
, for the first time, on Armistice Day 1937.