An Electron Telescope

Author: J.B. Hoag

With glass lenses, an image of a distant object is projected onto a photosensitized surface, as at the left of Fig. 21 0.

Fig. 21 0. An electron telescope

A set of positively charged metal rings focuses the electrons emitted from each point of the photocathode onto a fluorescent screen to give a visible image. Invisible ultra-violet or invisible near-infrared rays may be used instead of visible light rays.