Orthicon(redirected from Video camera tube)
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a television camera tube with a mosaic photocathode, in which the light image is converted into an electric image that is read by a beam of low-velocity electrons (secondary emission coefficient 1). The orthicon was proposed in 1939 by the American engineers. A. Rose and H. lams.
The image being transmitted is projected onto the target of the orthicon, which is a thin glass plate coated on the object side with a semitransparent, electrically conductive layer that serves as the signal plate; on the projector side the plate is coated with a fine-grained photoactive layer that is the mosaic photocathode. The photocurrent charges the elementary capacitors formed by the grains of the mosaic and the signal plate and thus forms a charge image on the surface of the target. Periodic discharge of the capacitors is brought about by an electron beam that scans the mosaic side of the target in a line-by-line pattern. At the same time, a video signal is formed in the circuit of the signal plate.
The transfer characteristic of an orthicon is almost linear over the whole operating range of illumination intensities. An orthicon is about 20 times more sensitive than an iconoscope, mainly because the photocurrent is used more efficiently in an orthicon. In the 1950’s the orthicon was replaced by the more advanced superorthicon.
A. A. ZHIGAREV