<title>Optical Systems For Direct View Night Vision Devices</title>

Abstract

Optical system designs specifically tailored for the high apertures required for direct view, passive, image intensifier, night vision systems began in the late fifties with a 14 inch focal length F/1.4 catadioptric objective. Three spherical corrector lenses were used in a flat field design for a 40mm image intensifier system. The principles developed proved quite successful, eventually leading to similar objectives used on most 40mm, 25mm, and 18mm format, first generation, night vision sighting telescopes. The principles are discussed and comparisons are made with several other high aperture catadioptric systems recently discussed in the literature. More compact second generation electrostatic and wafer type tubes opened new opportunities for light weight system designs. The 18mm microchannel plate wafer tube in particular resulted in a number of new viewing systems, including nairs of 1X wide angle telescopes used as night vision goggles. The nrinciples involved in these systems are described as well as the eyepiece performance and characteristics which are unusually important. For these eyepieces and in fact for all of the newer Magnifier eyepieces, Night Vision Laboratories has developed new methods of testing and criteria for specifications that require considerably better correction that had previously been required. The most recent development in the field of direct view night vision devices has been that of the Biocular eyepiece. The principles and characteristics of this rather successful innovation are discussed.