针对传统红外连续变焦系统难以同时满足高变倍比和大相对口径的使用要求, 通过采用复合变焦光学系统结构, 增加传统红外连续变焦光学系统的变焦距范围和相对口径。基于长波红外320×240像元、25 μm×25 μm非制冷焦平面探测器, 设计了一款高变倍比大相对口径长波红外变焦光学系统,光学系统由一个连续变焦部分与两档变焦部分组成, 通过引入衍射光学元件校正长焦端色差, 工作波段为8 μm～12 μm, 焦距变化范围为-9 mm～-272.25 mm, F数为1.4。该系统具有成像质量好、变倍比高、相对口径大、导程小和凸轮曲线平滑等优点。

For the traditional infrared continuous zoom system difficult to meet the requirements of high zoom ratio and large relative aperture simultaneously, the structure of compound zoom optical system is used to increase the range of focal length and relative aperture of the traditional infrared continuous zoom optical system. Based on the long-wave uncooled focal plane detector with the pixel number of 320×240 and the pixel size of 25 μm×25 μm, a high zoom ratio long-wave infrared(LWIR) zoom optical system was designed. The optical system consists of a continuous zoom system part and a two-step zoom system part. The diffractive optical element is utilized to correct the chromatic aberration at the long focal length of the system. The working band of the system is 8 μm to 12 μm, the range of the focal length is -9 mm to -272.25 mm, and the F number is 1.4. The system has such advantages as good imaging quality, high zoom ratio, large relative aperture, small lead and smooth cam curves.