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An electronic device for amplifying the brightness of an image. Amplification is achieved by the multistage production of photoelectrons. A photocathode is coated on the inside of the entry window. The electrons produced when a light signal strikes the window are accelerated through a potential of about 40 kV. Focusing is by the magnetic field of a surrounding solenoid combined with the electrostatic fields of ring electrodes; alternatively, the focusing may be entirely electrostatic. Further amplification is introduced by the use of more than one photocathode stage. The image finally formed on a phosphor screen is many times brighter than the original. The final detector may be a television camera or a charge-coupled device. A drawback of the system is the unavoidable distortion in the image; nevertheless, such devices have found wide application in astronomy.
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