中文摘要：

与红外连续变焦光学系统相比，红外两档变焦光学系统具有结构简单、装调容易、透射比高等优点。研究了红外两档变焦光学系统的设计方法并给出了具体设计实例，该系统采用轴向移动式变焦方式，设计结果表明，在-20℃-40℃的温度范围内，空间频率141p／mm处，宽视场和窄视场都具有良好的成像质量。

英文摘要：

Compared with the infrared continuous zoom optical system, infrared switch-zoom system has many advantages, suan as simple structure, easy fixing, high transmission and so on. The principle of infrared switch-zoom optical system is analyzed, and a example has been presented.The optical configuration is based on the axial motion of a lens group along the optical axis. When spatial frequency is 141p/mm, both the wide-FOV and narrow-FOV show high image quality in the temperature range -20℃-40℃.