Exposure area control for an optical scanning system for manufacturing cathode ray tubes

In a method of electrically controlling an optical scanning exposure system in manufacturing cathode ray tubes having a faceplate with a layer of photosensitive material thereon, said optical scanning exposure system including a light source with a wavelength spectrum for exposing the photosensitive material, means for scanning the faceplate with a light beam, and means for deflecting the light beam at a angle related to the angle of incidence of an electron beam in a cathode ray tube, and said electrical control system including an angle of incidence and scan rate memory means;

• a scan rate means for controlling scanning of the light beam, and an angle of incidence control means for controlling the angle of incidence of the light beam, said control method including the steps of activating the scan rate means to cause light beam scanning of the faceplate by said means for effecting horizontal and vertical scanning, applying signals representative of the positioned location of the scanning light beam to the angle of incidence and scan rate memory means, coupling signals representative of an angle of incidence of an electron beam at a particular positioned location to an angle of incidence deflection means, and coupling signals representative of a desired rate of scan to the scan rate means, the improvement comprising the step of
• providing a signal and combining the signal with the signals related to an angle of incidence of an electron beam at a particular positional location on the faceplate of a cathode ray tube and applying said combined signals to an angle of incidence deflector means to cause movement of the effective light beam in a virtual source plane and provide an increased area of partial exposure and a decreased area of full exposure of said faceplate whereby exposure area size and shape is controlled.