为了实现对有限远物体的快速对准和精确分辨，研制了物距280～340 mm的变焦距镜头，对该变焦距镜头的工作原理、结构设计和测试实验等进行了研究。详细阐述了该镜头的整体结构、变焦补偿机构和调焦机构，研究了变倍补偿凸轮和调焦凸轮的凸轮曲线，在NX NASTRAN软件环境下建立了变倍补偿凸轮和调焦凸轮的有限元模型，并对其进行了模态分析，得到了两个凸轮的前六阶固有频率和振型，其中两凸轮的一阶固有频率分别为1050 Hz和1132 Hz，满足系统固有频率的要求。采用EIA-1956分辨率标准测试板对研制的变焦距镜头分辨率进行了测试。实验结果表明，该变焦距镜头的水平分辨率优于800 TV-Line（电视线），满足设计指标要求。

In order to realize quick focusing and high resolutions for a limited distance object, a zoom lens with object distance of 280～340 mm is developed. Its working principle, structure design and testing experiment are researched. Then the details of the whole structure, the variable and compensation mechanism, and the focus adjusting mechanism of the zoom lens are introduced. The curves of variable/compensation cam and focus adjusting cam are studied, and their models are established with the software of NX NASTRAN. Additionally, mode analyses of both cams are finished and corresponding natural frequency and vibration mode are obtained from the 1st order to the 6th order, respectively. Result indicates that the 1st order natural frequencies of the cams are separately 1050 Hz and 1132 Hz, which meet the requirements of the natural frequency. By using the EIA-1956 resolution test chart, the lens resolution test experiment is carried out, which indicates that the horizontal resolution of the zoom lens is better than 800 TV-Line and matches the required design parameters.