根据深空探测任务中对着陆器相机要求宽探测范围的需求，设计了一种对焦结构可见/近红外相机光学系统.系统采用准远心光学结构，由前固定组和后对焦组组成，前固定组属于一个无焦系统，后对焦组放于固定组后，当对远近目标成像时，移动对焦组可在像面上获得清晰成像，并且不同距离的目标对焦过程中，系统的焦距不发生改变.实验测得系统焦距为50 mm，F数为8，谱段范围为400~1 000 nm，能实现探测范围从0.8 m到无穷远目标的清晰成像; 成像质量高，光学传递函数接近衍射极限，畸变优于1%.对光学系统的公差进行了分析，表明该光学系统公差在现有加工水平下均能保证良好的成像性能，具有工程可实现性.研究表明该光学系统可应用于月球、火星、小行星等深空探测中着陆器的中等焦距的立体测绘相机.

A optical system of lander optical payload was designed for the requirement of focusing on objects. A noval focusing type was made that the optical system could keep fixed focal length during focusing. An approaching telecentric optical structure is designed, the optical system was made up of front fixing lens unit and rear focusing lens unit. The front fixing lens is a kind of afocal optical system. The rear focusing lens is at the back of fixing lens unit. The optical can image objects from 0.8 m to infinity in focus by moving rear focusing lens unit. The optical system with spectral range from 400 to 1 000 nm, fixed focal length of 50 mm and F number of 8 can focus on objects located within the range of 0.8 meter to infinity. At last, The modulation transfer function of the optical system can reach to diffraction limit, and distortion is less 1%. The image quality can meet the requirement to the optical system. By the analysis of optical system tolerance, the optical system can keep good imaging quality after fabrication. The optical system can be used to explore moon, mars and asteroids.