Construction of Image Orthicon The figure below represents the structure of image orthicon: As it is clear from the above figure that the whole structure is divided into 3 sections which are as follows: Image section, Scanning section and Electron gun and multiplier section. The image section consists of photocathode formed by coating the inner surface of a glass faceplate with silver-antimony-cesium. A lens system is used that focuses the image from a scene on the surface of the photocathode. This incident light from the image allows the emission of electrons from the surface of the photocathode. The surface of the photocathode is semi-transparent in nature. Thereby allowing penetration of incidenting light into the inner surface from where the electron emission is taking place.
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The development of the CRT which could be used as an electronic replacement of the mechanical receiver forced the researchers to produce an electronic eye to replace the mechanical flying spot principle from Manfred von Ardenne which was more or less successfully used for the transmission of film in the beginning with 30 and later with scanlines.
Several inventors clamed to have the first ideas for single or double sided target camera pickup tubes, the Hungarian engineer Kolomon Tihanyi claimed the invention of the Iconoscope storage principle, which later was used by Zworykin. Several other people inbetween and claimed to file the first pickup tube patents like Francois Charles Pierre Henrouteau George J. Blake and Henry D. Farnsworth patented his all electronic TV system on Jan 7, By Sept 7, he was able to send a single horizontal line of light on the face of a CRT.
The dissector tube however, became never a successful television pickup device and was mainly used to scan film and dia-positives, this was the result of a lack of sensitivity, it was in fact a cold cathode tube. Kenjiro Takayanagi made the first camera tube for Japan and presented his all electronic TV system also in This was the beginning of the all electronic TV age, it was a race of patents which RCA eventually won.
With this arrangement ended the great struggle between Farnsworth and RCA. This could be seen as dark spots on the receiving image on the upper left and bottom left of the picture. The image of the Super Emitron was not formed by the photo-emission to the target plate itself, but by photo-electrons which came free by the illumination of a Photo Cathode in front of the target. This tube was much more efficient than the standard Iconoscope tube. Even more progress was made with the Riesel-Iconoscope.
In the Riesel tube there was a second photo sensitive Cathode in the form of a ring nearby the target. From this Cathode a constant flow of slow electrons was dripping to the target. Harley Ambrose Iams and Alberts Rose RCA developed in the Orthicon tube, although it was theoretically a simpler design than the Iconoscope, building this tube was much more difficult.
It took another five years to build a new and better one, the Image Orthicon. Development of the first 3" Image orthicon started in with the LM5 for the use in guided missiles followed by the smaller MIMO miniature image orthicon.
This was a great advance for the postwar TV industry, RCA presented the fist public demonstration Oct 25 , the production was extended for a short time with the building of the huge 4,5" Image orthicon which was even more sensitive but much larger than the former ones and also more expensive.
Image Orthicons were valued and insured for pounds at the BBC in , in those days a lot of money! To overcome this, the Vidicon tube was eventually developed in , there was no need to be superior to the Image orthicon, but to produce camera tubes in a more economic way. Vidicon tubes were used until when the first solid state CCD camera came on the market. Even today the Vidicon and Vidicon-like tubes are still used in the industrial, medical and military environment. Found in a flea market!
Probably all that is left today of this early Philips camera tube.
It is a sensitive tube and handling a wide range of light values and contrast. This tube makes use of the high photoemissive sensitivity obtainable from photocathodes, image multiplication at the target caused by secondary emission and an electron multiplier. It has three main sections: Image section Electron gun-cum-multiplier section. Image Section A photosensitive surface, called photocathode, acting as main transducer in image orthicon camera tube. A very large negative potential i.
Video camera tube
Main article: Image dissector An image dissector is a camera tube that creates an "electron image" of a scene from photocathode emissions electrons which pass through a scanning aperture to an anode , which serves as an electron detector. Farnsworth applied for a patent for his Television System that included a device for "the conversion and dissecting of light". Due to their poor light sensitivity, image dissectors were rarely used in television broadcasting, except to scan film and other transparencies. As light strikes the photocathode, electrons are emitted in proportion to the intensity of the light see photoelectric effect. The entire electron image is deflected and a scanning aperture permits only those electrons emanating from a very small area of the photocathode to be captured by the detector at any given time. The output from the detector is an electric current whose magnitude is a measure of the brightness of the corresponding area of the image.
Image Orthicon Camera Tube