Apparatus for use in determining a characteristic of a cathode ray tube

摘要

Test apparatus for a cathode ray tube has optical elements disposed along two optical paths from the screen of a cathode ray tube to two photosensors. One optical path passes through a graticule which has a pattern of light transmissive and non-transmissive areas. The real image of a luminous spot on the screen is accurately positioned on a boundary between two of the areas of the graticule by deriving a control signal from a comparison of the photosensor outputs.