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Ever since the gradient index (GRIN) materials came into existence, there have been continuous efforts by various research groups in the world to improve these materials and explore their potential for designing high-performance and compact optical systems. Recently, with the advent of a commercial gradient index glass such as GRADIUM by LightPath Technologies Inc., Arizona, USA, there has been an increased interest among optical engineers to use these materials for developing realizable GRIN systems. We have previously reported the use of GRADIUM in image intensifier tube based night vision systems such as passive night vision goggles for patrolling and passive night sights for drivers of armored vehicles. These applications generally use systems with unit magnification and large field of view. Derivatives of Double-Gauss configuration are best suited for the front-end objective lens of such systems. In this paper, we discuss the use of GRADIUM in night vision systems for long-range target recognition under low-level of illumination. These applications use image intensifier night vision systems for long-range target recognition under low-level of illumination. These applications use image intensifier night vision telescopes having certain desired magnifications. The front-end objectives used for such telescopes should have large focal lengths and high apertures generally in the range of 80mm to 140mm for meeting the range specifications for target recognition. Petzval type of configuration is typically used for realizing such large-aperture and low f-number objectives with high contrast at lower frequencies throughout the image field. Use of conventional glass elements in such systems often limits the off-axis performance. We demonstrate, in this paper, the potential of GRADIUM in improving the overall performance of a pair of conventional Petzval objectives used in night vision devices for long range observations.
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