大口径离轴折反式中波红外连续变焦系统设计

基于制冷型320240凝视焦平面阵列探测器，设计了大口径离轴折反式中波红外连续变焦光学焦系统。系统工作波段为3.7～4.8 m，焦距范围250～2 000 mm，F数为4。光学系统分离轴无光焦度系统和透射式连续变焦系统两部分设计，匹配对接后优化。解决了透射式连续变焦系统因材料限制不能做到大口径、共轴折反式连续变焦系统短焦遮拦比大和离轴三反不能做到100%冷光阑效率的缺陷。满足100%冷光阑效率，在空间频率16 lp/mm处系统的MTF值大于0.5，具有像质好，分辨率高等特点，满足设计要求。

Design of large aperture off-axis catadioptric middle infrared continuous zoom system

On the basics of a cool 320240 detector with staring focal plane array, a large aperture off-axis catadioptric middle infrared continuous zoom system was designed. The system worked at 3.7-4.8 m which achieved the zoom of 250 mm to 2 000 mm and F number of 4. The optical system was divided into two segments. Firstly, an off-axis aspheric non-power system as the front system was designed. Then the continuous zoom lens which matched with the non-power system as the back system was designed. Because of the material constraint, the refractive zoom system could not realize large aperture. Coaxal catadioptric zoom system had great block ratio. And three mirrors zoom system could not achieve cold shield efficiency 100%. The off-axis catadioptric zoom system cold account for forenamed limitation. The system cold offer a high resolution and excellent images, and its cold shield efficiency is 100%. The system satisfies the design requirements.