Image dissector

An image dissector, also called a dissector tube, is a video camera tube in which emissions create an "electron image" which is then scanned to produce an electrical signal representing the visual image. The term may apply specifically to a dissector tube employing magnetic fields to keep the electron image in focus, and an electron multiplier to scan the electrons. Dissectors were used only briefly in television systems before being replaced by the much more sensitive iconoscope during the 1930s.

American television pioneer Philo T. Farnsworth invented the first functional image dissector in 1927. Earlier, German Professor Max Dieckmann and his student Rudolf Hell filed in 1925 a patent for a device named Lichtelektrische Bildzerlegerröhre für Fernseher (Photoelectric Image Dissector Tube for Television) that worked along the same principles, but failed to reduce it to practice.

An image dissector focuses a visual image onto a layer of photosensitive material, such as caesium 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 "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 suitably representative of 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.

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