IMAGE INTENSIFIERS
Electronic image intensifiers do as their name implies, they intensify, or amplify, the light from weak sources of radiation. I n one such system photons from the telescope are focused onto a photocathode surface, which ejects electrons. The electrons are increased in number, accelerated, and focused by means of electric and magnetic fields onto a phosphorescent screen, which emits a spark of light for each electron that strikes it. Thus the faint light from the astronomical source is amplified by the device into light sufficient to record the image on a photographic plate. Alternatively a computer circuit can be used to count the electrons during the exposure. Still other image-intensifying techniques are in use or in developmental stages; these techniques can reduce exposure times by factors of 50 to 100 over those for photographic systems.
