摘要:
Protection of a low level television camera tube used with an image intensifier tube is provided by a shutter and a current limiting element in series with the photocathode of the image intensifier tube to cause the electron image in the intensifier to defocus, thereby providing protection for the camera tube while the shutter is being closed. A current limiting element in series with the photocathode of the camera tube further aids in protecting the target of the camera tube by reducing the kinetic energy of photoelectrons produced in response to a light image from the intensifier. A photodetector responds to excessive illumination to cause a control circuit to close the shutter.