Optical Design Of Long Wave Infrared Zoom System

In recent years, Infrared imaging technology has been used in the military affairs (infrared warning, tracking, aiming and guidance)and the civilian areas (electrical power system, fire protection, medical diagnosis, forest fire early warning, search for smuggler, night security monitoring, search and rescue), and the continuous zoom system has been used more and more widely, which makes it is easy to realize the function of searching target in large field of view and distinguishing target in small field view. For target recognition and tracking, especially for high-speed motion target, continuous zoom system has the advantage of not missing target in field of view during the switching process, its favorable for the photoelectric detection and reconnaissance.An infrared zoom optical system is designed based on the optical zoom theory, even aspheric and diffractive optical element are used to balance the aberration. The focal plane array(FPA) detector is of320×240pixels and25×25μm pixel pitch. The working waveband of this optical system is8μm～12μm, F number is less than1and zoom ratio is3:1.The system consists of4groups and4lenses. There are5aspheric surfaces and1diffractive surface in the system. The optical system is optimized and its image quality is evaluated with ZEMAX. The results show that the MTF in the whole focal range approaches the diffractive limit at the Nyquist frequency of201p/mm.