Iconoscope
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The iconoscope (from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
: ''εἰκών'' "image" and ''σκοπεῖν'' "to look, to see") was the first practical
video camera tube Video camera tubes were devices based on the cathode ray tube that were used in television cameras to capture television images, prior to the introduction of charge-coupled device (CCD) image sensors in the 1980s. Several different types of tubes ...
to be used in early
television camera A professional video camera (often called a television camera even though its use has spread beyond television) is a high-end device for creating electronic moving images (as opposed to a movie camera, that earlier recorded the images on film). O ...
s. The iconoscope produced a much stronger signal than earlier mechanical designs, and could be used under any well-lit conditions. This was the first fully electronic system to replace earlier cameras, which used special spotlights or spinning disks to capture light from a single very brightly lit spot. Some of the principles of this apparatus were described when
Vladimir Zworykin Vladimir Kosma Zworykin; or with the patronymic as ''Kosmich''; or russian: Кузьмич, translit=Kuz'mich, label=none. Zworykin anglicized his name to ''Vladimir Kosma Zworykin'', replacing the patronymic with the name ''Kosma'' as a middle na ...
filed two patents for a ''television system'' in 1923 and 1925. A research group at
RCA The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...
headed by 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 Telefunken was a German radio and television apparatus company, founded in Berlin in 1903, as a joint venture of Siemens & Halske and the ''Allgemeine Elektrizitäts-Gesellschaft'' (AEG) ('General electricity company'). The name "Telefunken" app ...
bought the rights from RCA and built the superikonoskop camera used for the historical TV transmission at the
1936 Summer Olympics The 1936 Summer Olympics (German: ''Olympische Sommerspiele 1936''), officially known as the Games of the XI Olympiad (German: ''Spiele der XI. Olympiade'') and commonly known as Berlin 1936 or the Nazi Olympics, were an international multi-sp ...
in Berlin. The iconoscope was replaced in Europe around 1936 by the much more sensitive Super-Emitron and Superikonoskop, while in the United States the iconoscope was the leading camera tube used for broadcasting from 1936 until 1946, when it was replaced by the
image orthicon tube Video camera tubes were devices based on the cathode ray tube that were used in television cameras to capture television images, prior to the introduction of charge-coupled device (CCD) image sensors in the 1980s. Several different types of tub ...
.


Operation

The main image forming element in the iconoscope was a
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
plate with a pattern of photosensitive granules deposited on the front using an electrically insulating glue. The granules were typically made of
silver Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...
grains covered with
caesium Caesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that a ...
or
caesium oxide Caesium oxide (IUPAC name), or cesium oxide, describes inorganic compounds composed of caesium and oxygen. Several binary (containing only Cs and O) oxides of caesium are known.. Caesium oxide may refer to: * Caesium suboxides (Cs7O, Cs4O, and Cs1 ...
. The back of the
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
plate, opposite the granules, was covered with a thin film of silver. The separation between the silver on the back of the plate and the silver in the granules caused them to form individual
capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...
s, able to store electrical charge. These were typically deposited as small spots, creating
pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...
s. The system as a whole was referred to as a "mosaic". The system is first charged up by scanning the plate with an
electron gun An electron gun (also called electron emitter) is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode-ray tubes (CRTs), used in nearly ...
similar to one in a conventional television cathode ray display tube. This process deposits charges into the granules, which in a dark room would slowly decay away at a known rate. When exposed to light, the photosensitive coating releases electrons which are supplied by the charge stored in the silver. The emission rate increases in proportion to the intensity of the light. Through this process, the plate forms an electrical analog of the visual image, with the stored charge representing the inverse of the average brightness of the image at that location. When the
electron beam Cathode rays or electron beam (e-beam) are streams of electrons observed in discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to ele ...
scans the plate again, any residual charge in the granules resists refilling by the beam. The beam energy is set so that any charge resisted by the granules is reflected back into the tube, where it is collected by the collector ring, a ring of metal placed around the screen. The charge collected by the collector ring varies in relation to the charge stored in that location. This signal is then amplified and inverted, and then represents a positive video signal. The collector ring is also used to collect electrons being released from the granules in the
photoemission The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, and solid sta ...
process. If the gun is scanning a dark area few electrons would be released directly from the scanned granules, but the rest of the mosaic will also be releasing electrons that will be collected during that time. As a result, the black level of the image will float depending on the average brightness of the image, which caused the iconoscope to have a distinctive patchy visual style. This was normally combatted by keeping the image continually and very brightly lit. This also led to clear visual differences between scenes shot indoors and those shot outdoors in good lighting conditions. As the electron gun and the image itself both have to be focused on the same side of the tube, some attention has to be paid to the mechanical arrangement of the components. Iconocopes were typically built with the mosaic inside a cylindrical tube with flat ends, with the plate positioned in front of one of the ends. A conventional movie camera lens was placed in front of the other end, focused on the plate. The electron gun was then placed below the lens, tilted so that it was also aimed at the plate, although at an angle. This arrangement has the advantage that both the lens and electron gun lie in front of the imaging plate, which allows the system to be compartmentalized in a box-shaped enclosure with the lens completely within the case. As the electron gun is tilted compared to the screen, its image of the screen is not as a rectangular plate, but a keystone shape. Additionally, the time needed for the electrons to reach the upper portions of the screen was longer than the lower areas, which were closer to the gun. Electronics in the camera adjusted for this effect by slightly changing the scanning rates."1945 RCA CRV-59AAE Iconoscope Camera"
LabGuy's World
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

The problem of low sensitivity to light resulting in low electrical output from transmitting or "camera" tubes would be solved with the introduction of charge-storage technology by the Hungarian engineer
Kálmán Tihanyi Kálmán Tihanyi or in English language technical literature often mentioned as Coloman Tihanyi or Koloman Tihanyi (28 April 1897 – 26 February 1947) was a Hungarian physicist, electrical engineer and inventor. One of the early pioneers o ...
in the beginning of 1925."Kálmán Tihanyi (1897–1947)", ''IEC Techline''
International Electrotechnical Commission (IEC), 2009-07-15.
His solution was a camera tube that accumulated and stored electrical charges ("photoelectrons") within the tube throughout each scanning cycle. The device was first described in a patent application he filed in
Hungary Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Croatia a ...
in March 1926 for a television system he dubbed "Radioskop"."Kálmán Tihanyi's 1926 Patent Application 'Radioskop'"
''Memory of the World'', United Nations Educational, Scientific and Cultural Organization (
UNESCO The United Nations Educational, Scientific and Cultural Organization is a specialized agency of the United Nations (UN) aimed at promoting world peace and security through international cooperation in education, arts, sciences and culture. It ...
), 2005, retrieved 2009-01-29.
After further refinements included in a 1928 patent application, Tihanyi's patent was declared void in Great Britain in 1930,Tihanyi, Koloman, ''Improvements in television apparatus''
European Patent Office, Patent No. GB313456. Convention date UK application: 1928-06-11, declared void and published: 1930-11-11, retrieved: 2013-04-25.
and so he applied for patents in the United States.
Zworykin Vladimir Kosma Zworykin; or with the patronymic as ''Kosmich''; or russian: Кузьмич, translit=Kuz'mich, label=none. Zworykin anglicized his name to ''Vladimir Kosma Zworykin'', replacing the patronymic with the name ''Kosma'' as a middle na ...
presented in 1923 his project for a totally electronic television system to the general manager of Westinghouse. 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
colloid A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...
al deposit of photoelectric material (
potassium hydride Potassium hydride, KH, is the inorganic compound of potassium and hydrogen. It is an alkali metal hydride. It is a white solid, although commercial samples appear gray. It is a powerful superbase that is useful in organic synthesis. It is sold com ...
) 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 Westinghouse, and Zworykin was asked ''to work on something useful''. A patent for a television system was also filed by
Zworykin Vladimir Kosma Zworykin; or with the patronymic as ''Kosmich''; or russian: Кузьмич, translit=Kuz'mich, label=none. Zworykin anglicized his name to ''Vladimir Kosma Zworykin'', replacing the patronymic with the name ''Kosma'' as a middle na ...
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. 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 Sir Isaac Shoenberg (1 March 1880 – 25 January 1963) was a British electronic engineer born in Belarus who was best known for his role in the history of television. He was the head of the EMI research team that developed the 405-line (Marconi-EM ...
applied for a patent for a new device they dubbed "the emitron", a 405-line broadcasting service employing the super-emitron began at studios in
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in 1936, and a patent was issued in the US in 1937. Meanwhile, in 1933,
Philo Farnsworth Philo Taylor Farnsworth (August 19, 1906 – March 11, 1971) was an American inventor and television pioneer. He made many crucial contributions to the early development of all-electronic television. He is best known for his 1927 invention of t ...
had also applied for a patent for a device that used a charge storage plate and a low-velocity electron scanning beam. A corresponding 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 4 ft-c (43 lx) and 20 ft-c (215 lx). 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. In Britain, a team formed by engineers Lubszynski, Rodda, and MacGee developed the super-emitron (also superikonoscop in Germany and image iconoscope in the Netherlands) in 1934, this new device was between ten and fifteen times more sensitive than the original emitron and iconoscope, and it was used for a public broadcasting by the
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...
, for the first time, on Armistice Day 1937. The image iconoscope was the representative of the European tradition in electronic tubes competing against the American tradition represented by the image orthicon.


See also

*
Image dissector An image dissector, also called a dissector tube, is a video camera tube in which photocathode emissions create an "electron image" which is then swept up, down and across an anode to produce an electrical signal representing the visual image. It e ...
*
Video camera tube Video camera tubes were devices based on the cathode ray tube that were used in television cameras to capture television images, prior to the introduction of charge-coupled device (CCD) image sensors in the 1980s. Several different types of tubes ...


References


External links


Iconoscope history
{{Electronic components History of television Russian inventions Television technology