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An image dissector, also called a dissector tube, is a
Cambridge University Press, 1989, pp. 1000-1001. . The term had also been used for other kinds of early video camera tubes. Dissectors were used only briefly in television systems before being replaced by the much more sensitive
Patent No. 1,773,980, U. S. Patent Office, filed 1927-01-07, issued 1930-04-26. Retrieved 2010-03-12. On September 7 of that year, the image dissector successfully transmitted its first image, a simple straight line, at Farnsworth's laboratory at 202 Green Street in
''The TIME 100: Scientists & Thinkers'', TIME.com, 1999-03-29, retrieved 2009-07-28.
, ''The Virtual Museum of the City of San Francisco'', retrieved 2009-07-15. By September 3, 1928, Farnsworth had developed the system sufficiently to hold a demonstration for the press, the first such successful demonstration of a fully electronic television system. In 1929 Farnsworth eliminated a motor generator from the system, so it then had no mechanical parts. Further developments that year included improvements in image clarity and an increase in the number of lines of resolution, such that it exceeded that of the mechanical television systems. Also in 1929, Farnsworth transmitted the first live human images with his system, including a three and a half-inch image of his wife Elma ("Pem") with her eyes closed (possibly due to the bright lighting required). Since the electrons emitted within an image dissector are collected by the electron multiplier or anode only during the very brief time an area of the "electron image" is exposed, the bulk of the electrons are lost. Thus the earliest image dissectors were very inefficient, and extremely bright illumination was required for it to be used effectively. Farnsworth addressed this problem with the invention of an "electron multiplier" (not to be confused with contemporary
Patent No. 1,969,399, U. S. Patent, filed 1930-03-03, issued 1934-08-07. Retrieved 2010-03-12. Farnsworth applied for a patent for his "electron multiplier" on March 3, 1930 and demonstrated its application in 1931.Abramson, Albert (1987), ''The History of Television, 1880 to 1941''. Jefferson, NC: Albert Abramson. p. 148. .Everson, George (1949), ''The Story of Television, The Life of Philo T. Farnsworth'' New York, NY: W. W. Norton & Co,. . Farnsworth continued to improve the device, which would come to be called a " multipactor",Farnsworth, Philo T., ''Multipactor Phase Control''
Patent No. 2,071,517, U. S. Patent Office, filed 1935-05-07, issued 1937-02-23. Retrieved 2010-03-12. such that it reportedly could amplify a signal to the 60th power or better, and showed great promise in other fields of electronics. A significant problem with the multipactor, however, was that it wore out at an unsatisfactorily rapid rate. On August 25, 1934, Farnsworth gave the world's first public demonstration of a complete, all-electronic television system, which included his image dissector, at theNew Television System Uses 'Magnetic Lens'
, ''Popular Mechanics'', Dec. 1934, p. 838–839.Burns, R. W. ''Television: An international history of the formative years''. (1998). IEE History of Technology Series, 22. London: IEE, p. 370. . In April 1933, Farnsworth submitted a patent application entitled ''Image Dissector'', but which actually detailed a charge storage low electron velocity
Patent No. 2,087,683, U. S. Patent Office, filed 1933-04-26, issued 1937-07-20. Retrieved 2010-03-12. Its principles were developed and implemented by RCA (which paid royalties for them) in the image orthicon, the mainstay commercial television camera tube until it began to be replaced by solid state image sensors in the 1980's. By late 1930s, dissectors were replaced by more efficient
The Farnovision - history of Philo Farnsworth and invention of the Image Dissector"Farnsworth's Image Dissector"IEEE Global History Network
An image dissector, also called a dissector tube, is a 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 ...
in which photocathode
A photocathode is a surface engineered to convert light (photons) into electrons using the photoelectric effect. Photocathodes are important in accelerator physics where they are utilised in a photoinjector to generate high brightness electron be ...
emissions create an "electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have n ...
image" which is then swept up, down and across an anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
to produce an electrical signal representing the visual image. It employs magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
s to keep the electron image in focus, and later models used electron multiplier
An electron multiplier is a vacuum-tube structure that multiplies incident charges. In a process called secondary emission, a single electron can, when bombarded on secondary-emissive material, induce emission of roughly 1 to 3 electrons. If an ...
to pick up the electrons.Horowitz, Paul and Winfield Hill, ''The Art of Electronics'', Second EditionCambridge University Press, 1989, pp. 1000-1001. . The term had also been used for other kinds of early video camera tubes. Dissectors were used only briefly in television systems before being replaced by the much more sensitive
iconoscope
The iconoscope (from the Greek: ''εἰκών'' "image" and ''σκοπεῖν'' "to look, to see") was the first practical video camera tube to be used in early television cameras. The iconoscope produced a much stronger signal than earlier mec ...
during the 1930s. They continued to be used for imaging in early weather satellites and the Lunar lander
A lunar lander or Moon lander is a spacecraft designed to land on the surface of the Moon. As of 2021, the Apollo Lunar Module is the only lunar lander to have ever been used in human spaceflight, completing six lunar landings from 1969 to 19 ...
, and for star attitude
Attitude may refer to:
Philosophy and psychology
* Attitude (psychology), an individual's predisposed state of mind regarding a value
* Metaphysics of presence
* Propositional attitude, a relational mental state connecting a person to a propo ...
tracking in the Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program n ...
and the International Space Station
The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos ( ...
.
Operation
An image dissector focuses a visual image onto a layer of photosensitive material, such as cesium oxide, which emits negatively charged "photoelectrons" proportional to the intensity of the light striking the material.Electrostatic
Electrostatics is a branch of physics that studies electric charges at rest ( static electricity).
Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for ...
deflecting plates or magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
s then periodically manipulate the resulting electron image horizontally and vertically before an electron multiplier
An electron multiplier is a vacuum-tube structure that multiplies incident charges. In a process called secondary emission, a single electron can, when bombarded on secondary-emissive material, induce emission of roughly 1 to 3 electrons. If an ...
, or a small aperture leading to a positively charged detector, or just an anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
, in the case of the earliest dissector tubes. The electron multiplier or aperture permits only those electrons emanating from a very small area of the electron image, representing a similarly small area of the visual image. The entire image is scanned several times per second to produce an electrical signal that represented a moving visual image.
Because the dissector does not store charge, it is useful for viewing the inside of furnaces and monitoring welding systems as it does not suffer from the "flare" normal picture tubes experience when looking at intense lights.
History
In April 1925, German professor Max Dieckmann and his studentRudolf Hell
Rudolf Hell (19 December 1901 – 11 March 2002) was a German inventor and engineer.
Career
Hell was born in Eggmühl. From 1919 to 1923, he studied electrical engineering in Munich. He worked there from 1923 to 1929 as assistant of Prof. Ma ...
applied for a patent for a device named Lichtelektrische Bildzerlegerröhre für Fernseher (Photoelectric Image Dissector Tube for Television). A patent was issued in October 1927, and their experiments were announced in the magazines ''Discovery'' and ''Popular Radio'', but they failed to reduce it to practice. In 1951, Hell claimed that he had made a tube but could not get it to function, since at the time there was an insufficient knowledge of electron optics
Electron optics is a mathematical framework for the calculation of electron trajectories along electromagnetic fields. The term ''optics'' is used because magnetic and electrostatic lenses act upon a charged particle beam similarly to optical le ...
, the manipulation of an 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 el ...
by electric
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...
or magnetic
Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particl ...
fields.
American television
Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, ...
pioneer Philo T. Farnsworth invented the first functional image dissector in 1927, submitting a patent application on January 7, 1927.Farnsworth, Philo T., ''Television System''Patent No. 1,773,980, U. S. Patent Office, filed 1927-01-07, issued 1930-04-26. Retrieved 2010-03-12. On September 7 of that year, the image dissector successfully transmitted its first image, a simple straight line, at Farnsworth's laboratory at 202 Green Street in
San Francisco
San Francisco (; Spanish for " Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the fourth most populous in California and 17t ...
.Postman, Neil, "Philo Farnsworth"''The TIME 100: Scientists & Thinkers'', TIME.com, 1999-03-29, retrieved 2009-07-28.
, ''The Virtual Museum of the City of San Francisco'', retrieved 2009-07-15. By September 3, 1928, Farnsworth had developed the system sufficiently to hold a demonstration for the press, the first such successful demonstration of a fully electronic television system. In 1929 Farnsworth eliminated a motor generator from the system, so it then had no mechanical parts. Further developments that year included improvements in image clarity and an increase in the number of lines of resolution, such that it exceeded that of the mechanical television systems. Also in 1929, Farnsworth transmitted the first live human images with his system, including a three and a half-inch image of his wife Elma ("Pem") with her eyes closed (possibly due to the bright lighting required). Since the electrons emitted within an image dissector are collected by the electron multiplier or anode only during the very brief time an area of the "electron image" is exposed, the bulk of the electrons are lost. Thus the earliest image dissectors were very inefficient, and extremely bright illumination was required for it to be used effectively. Farnsworth addressed this problem with the invention of an "electron multiplier" (not to be confused with contemporary
electron multiplier
An electron multiplier is a vacuum-tube structure that multiplies incident charges. In a process called secondary emission, a single electron can, when bombarded on secondary-emissive material, induce emission of roughly 1 to 3 electrons. If an ...
s), a device that increased the number of electrons in a circuit by generating "secondary emissions" of electrons from a pair of opposed surfaces, thus amplifying the electrical signal.Farnsworth, Philo T., ''Electron Multiplier''Patent No. 1,969,399, U. S. Patent, filed 1930-03-03, issued 1934-08-07. Retrieved 2010-03-12. Farnsworth applied for a patent for his "electron multiplier" on March 3, 1930 and demonstrated its application in 1931.Abramson, Albert (1987), ''The History of Television, 1880 to 1941''. Jefferson, NC: Albert Abramson. p. 148. .Everson, George (1949), ''The Story of Television, The Life of Philo T. Farnsworth'' New York, NY: W. W. Norton & Co,. . Farnsworth continued to improve the device, which would come to be called a " multipactor",Farnsworth, Philo T., ''Multipactor Phase Control''
Patent No. 2,071,517, U. S. Patent Office, filed 1935-05-07, issued 1937-02-23. Retrieved 2010-03-12. such that it reportedly could amplify a signal to the 60th power or better, and showed great promise in other fields of electronics. A significant problem with the multipactor, however, was that it wore out at an unsatisfactorily rapid rate. On August 25, 1934, Farnsworth gave the world's first public demonstration of a complete, all-electronic television system, which included his image dissector, at the
Franklin Institute
The Franklin Institute is a science museum and the center of science education and research in Philadelphia, Pennsylvania. It is named after the American scientist and statesman Benjamin Franklin. It houses the Benjamin Franklin National Memori ...
in Philadelphia, Pennsylvania
Philadelphia, often called Philly, is the largest city in the Commonwealth of Pennsylvania, the sixth-largest city in the U.S., the second-largest city in both the Northeast megalopolis and Mid-Atlantic regions after New York City. Since ...
., ''Popular Mechanics'', Dec. 1934, p. 838–839.Burns, R. W. ''Television: An international history of the formative years''. (1998). IEE History of Technology Series, 22. London: IEE, p. 370. . In April 1933, Farnsworth submitted a patent application entitled ''Image Dissector'', but which actually detailed a charge storage low electron velocity
cathode ray tube
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms ( oscilloscope), ...
(CRT) camera tube.Farnsworth, Philo T., ''Image Dissector''.Patent No. 2,087,683, U. S. Patent Office, filed 1933-04-26, issued 1937-07-20. Retrieved 2010-03-12. Its principles were developed and implemented by RCA (which paid royalties for them) in the image orthicon, the mainstay commercial television camera tube until it began to be replaced by solid state image sensors in the 1980's. By late 1930s, dissectors were replaced by more efficient
iconoscope
The iconoscope (from the Greek: ''εἰκών'' "image" and ''σκοπεῖν'' "to look, to see") was the first practical video camera tube to be used in early television cameras. The iconoscope produced a much stronger signal than earlier mec ...
s.
References
External links
The Farnovision - history of Philo Farnsworth and invention of the Image Dissector
See also
*Iconoscope
The iconoscope (from the Greek: ''εἰκών'' "image" and ''σκοπεῖν'' "to look, to see") was the first practical video camera tube to be used in early television cameras. The iconoscope produced a much stronger signal than earlier mec ...
*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 tubes ...
{{DEFAULTSORT:Image Dissector
History of television