本文根据某远红外变焦光学系统的技术指标要求：波长为8m ～ 12m、焦距为60nm ～ 240mm的4倍连续变焦功能、F/#为1.5、短焦视场大于10°，研究了各种变焦光学系统的结构形式和各种结构形式的 优缺点，分析了变焦系统的变倍方式。另外，研究了非球面设计的特点，并将其成功引入该变焦系统的设计。最后，系统采用锗为 材料，选择负组机械补偿，仅通过单一镜片的变倍组和补偿组的轴向移动，就可满足变倍和像质要求。引入非球面后的结果表 明，非球面不仅能简化系统结构、减轻系统重量，而且能有效提高系统的像质，是提高远红外变焦光学系统性能的有效途径之一。

According to the specifications of a far infrared zoom optical system: a 8m ～ 12m spectral region, continuous zoom from 60mm to 240mm, F/# of 1.5 and the short-focus field of view greater than 10°, the structures of various kinds of zoom optical systems and their advantages and disadvantages are studied. The zoom methods of those zoom systems are analyzed. In addition, the aspheric surface is studied and is successfully used in the design of a zoom system. Finally, because the germanium lenses and negative compensating zoom lenses are used, the zoom system can meet the requirements of zoom and image quality merely by moving the magnification and compensation units of a single lens axially. The result shows that the aspheric surface not only can simplify and reduce the structure and weight of the system respectively, but also can effectively improve the image quality of the system. This method is one of the effective approaches for improving the performance of far-infrared zoom optical systems.