- Image dissector
The image dissector was an early all-electronic television camera tube invented by
Philo Farnsworth .Most experimental television systems in the 1920s and 1930s made use of an electromechanical system, usually a
Nipkow disk combined with a single photoelectric cell for scanning an image and creating an electrical output. A similar device operating in reverse was used to project the image onto the picture screen.In 1922, Philo Farnsworth, a teenage farmboy in Utah, discovered that one could use a cathode ray tube to generate an electrical television signal without the need for a mechanical scanning device. The image dissector focused an image onto a layer of caesium oxide, which emitted electrons proportional to the intensity of the light. Only a small portion of the electron stream passed through an aperture to the electron collecting plate, representing a single point of the television image. Electromagnets were used to focus and deflect the electrons so that the total image was sequentially scanned.
Farnsworth's image dissector was successfully demonstrated and patent applications were made in 1927. This was the first successful demonstration of a fully electronic television system. Farnsworth continued making improvements to his system, and by 1929, image clarity and number of lines of resolution exceeded the achievements of the mechanical television systems.
The image dissector is not very efficient because the bulk of the electrons produced do not pass through the aperture and are discarded. Very bright lighting is required for it to be used as a television camera.
The
Iconoscope invented byVladimir Zworykin improved on Farnsworth's invention by combining the photosensitive material at each point with a capacitor so that all the electrons were captured. A separate beam of electrons was then used to scan over the image surface, resulting in an electrical current proportional to the quantity of stored electrons at each point.The Farnsworth image dissector was commercially produced for applications where very bright lighting existed, such as monitoring the interior of industrial furnaces.
Farnsworth also earned income from the production of the Iconoscope television cameras, because Zworykin's device was based on several patents that Farnsworth owned.
External links
* [http://www.farnovision.com/index.html The Farnovision - history of Philo Farnsworth and invention of the Image Dissector]
* [http://www.ieee-virtual-museum.org/collection/tech.php?id=2345850&lid=1 Farnsworth's Image Dissector]
* [http://www.google.com/patents?id=sDNIAAAAEBAJ U.S. patent] , filed 1933, issued 1937.
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