| Abstract: In the paper, based on the specifications of the far-infrared zoom optics for a detection system：the optical system with 8～12μm spectral region can realize the focal from 60～240mm continuous zoom; The F number of the system is 1.5; in the short focal mode, the field of view should be bigger than 10 . The researches have been made, including many types of the initial layout of zoom optical system and the advantages and the disadvantages of them. The zoom method has been analyzed. Then, aspheric surface not only has been studied, also is successfully used in the design of the system. At last, the result of the system uses germanium lenses and negative compensating zoom lens. When magnification unit and compensation unit--both of composition of them are one single lens--move, the system can meet the requirement of magnification and image quality. The design result, which contains aspheric surface, shows that aspheric surface not only has the function of simplifying the configuration and lightening the weight, also can improve the image quality markedly, which is one of the effective approaches of improving the performance of far-infrared zoom optical system. |