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 employs magnetic fields to keep the electron image in focus, and later models used electron multiplier to pick up the electrons. The term had also been used for other kinds of early video camera tubes. Dissectors were used only briefly for research in television systems before being replaced by different much more sensitive tubes based on the charge-storage phenomenon like the iconoscope during the 1930s. Despite the camera tubes based on the idea of image dissector technology were quickly and completely fallen out of use on the field of Television broadcasting, they continued to be used for imaging in early weather satellites and the Lunar lander, and for star attitude tracking in the Space Shuttle and the International Space Station. 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 deflecting plates or magnetic fields then periodically manipulate the resulting electron image horizontally and vertically before an electron multiplier, or a small aperture leading to a positively charged detector, or just an anode, 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.