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Measurement Of Veiling Glare In 2nd Generation Image Intensifiers

The presence of veiling glare in an image intensifier contributes to the total veiling glare of a complete passive direct view night vision system, it is therefore necessary during the development of an image intensifier to understand the various mechanisms which contribute to the total veiling glare. Second generation intensifiers are designed to operate at relatively low values of screen luminance and have saturation characteristics. Consequently the veiling glare measurement technique requires the accurate measurment of extremely low values of screen luminance (typically 0.01 cd/m2). The paper describes a sensitive scanning system developed to measure the veiling glare, and explains that the veiling glare is only partly optical in origin, there being a contribution from electron backscattering at the input surface of the channel plate electron mutliplier. The veiling glare caused by the back scattered electrons from the channel plate is critically dependent upon the electron optical design of the intensifier and the condition of the surface layer of the input to the channel plate. The measurement technique to be described has been a useful tool in helping to optimise the design of an 18mm low distortion 2nd generation intensifier.