An image tube with built in electrostatic zoom lens

During recent years zoom-lenses have been increasingly used in film and television cameras, instead of the more conventional lens-turret. In those cases where the optical image is fed to an image tube, such as an image converter or a television camera tube with image section, the same effect of continuously variable magnification of the image can be achieved electronically while employing a single optical lens with fixed focal length. This is possible by varying the magnification of the electron image in the tube as determined by the electron optical focusing system.