设计了一种大变倍比折射/衍射混合切换式变焦光学系统。该光学系统的工作波段为3.7～4.8mm，焦距为40 mm、120 mm 和360 mm，变倍比为9:1。系统采用切换式变倍方式，长焦时无变倍组，系统透过率高，作用距离远，切换时间短。该系统采用衍射元件消色差，减少了透镜的使用数量，提高了系统的整体性能。该系统在红外搜索、侦察等领域得到广泛应用。

A large zoom ratio of refractive/diffractive hybrid switching zoom optical system is designed in this paper. The operating waveband of this optical system is 3.7-4.8mm. The focal length is 40 mm, 120 mm and 360 mm, and the zoom ratio is 9: 1. A switching zoom mode is adopted in this system. The system has no zoom group at long focus. The system has advantages such as high transmittance, long operating distance, and short switching time. The diffractive elements are used to eliminate chromatic aberration in this system, which decreases the number of lenses, and improves the overall performance of this system. The proposed optical system has a wide application in infrared search and reconnaissance field.