随着无人机光电吊舱向小型化发展，对其变焦系统提出小型化、快速化的要求。本文设计了一种小型分段变焦系统。利用步进电机和透过型光遮断传感器构成调焦组件，设计了系统硬件电路和调焦算法，实现了光学镜头的快速分段变焦和焦距值的实时输出。系统采用离线方式标定聚焦点位置和焦距值，标定过程中使用 Tenengrad函数、Brenner函数、平方梯度函数判断出聚焦点位置，同时利用自准直法测焦仪测量镜头的焦距值。最终实现变焦系统重量小于 100 g，焦距值误差小于 1%，短焦与长焦的切换时间小于 1.7 s。

With miniaturization of the UAV of optoelectronic pod, the requirements of miniaturization and rapidity for its zoom system is raised. A small segmented zoom system is designed. The focusing components include stepper motor and permeability type of photo interrupter, and the hardware circuit of system and focus method is designed, which achieves the rapid segmented zoom of the optical lens and the real-time output of focal-length. The focal point position and focal length of system are calibrated by off-line methods. Tenengrad function, Brenner function and square gradient function are utilized to evaluate comprehensively during the calibration process of the focal point position. At the same time，it adopt auto collimation measured focus instrument to calibrate accurately the focal length of lens. Finally, it is achieved that this zoom system weighs less than 100 grams, the errors of focal-length is less than 1%, and the switching time between short focal and long focal is less than 1.7 seconds.