针对像元尺寸为17 m×17 m的 非致冷型640×480元探测器，基于补偿组兼顾调焦群作用的Varifocal 结构，仅用4片透镜就设计出了一种变倍比为6×的长波红外连续变焦光学 系统。针对低成本、高透波率的指标要求，通过理论计算得到了初始结 构，并用CodeV软件对其像差进行了优化，最后针对设计结果进行了 凸轮曲线求解和像质评价。结果表明，当 工作在8 ～ 12 m波段时，在相对孔径1.4 : 1保持不变的条件下，该系统实 现了焦距从20 mm到120 mm的连续变焦，而且空间频率20 lp/mm处的调 制传递函数(Modulation Transfer Function, MTF)值均大于0.5。通过样机实测发现，该系统 具有变倍比大、结构紧凑和分辨率高等特点，因而适用于红外监控设 备。

According to a 640×480 uncooled detector with pixel size of 17 m×17 m, a long wavelength infrared varical optical system with varifocal ratio of 6× is designed with only 4 lenses. To meet the requirements of low cost and high transmission, an initial configuration is obtained through theoretical calculation. The aberration of the initial configuration is optimized by using the CodeV software. Finally, cam curve solution and image quality evaluation are carried out for the design result. The result shows that when the relative aperture of 1.4: 1 is kept, the optical system can realize continuous zooming from 20 mm to 120 mm in the 8 to 12 m waveband. The Modulation Transfer Function (MFT) at the spatial frequency of 20 lp/mm is greater than 0.5. It is found in the actual measurement of the prototype that the optical system has the features of large zooming ratio, compact configuration and high resolution. It is suitable for infrared monitoring systems.