紧凑型双视场可见光镜头设计

为使观瞄系统以简单、紧凑结构实现探测、识别目标功能，选用光学补偿法设计紧凑型双视场可见光镜头。首先，根据视场、作用距离指标完成相机选型和焦距计算，依据已选相机像元尺寸和最低照度计算F数，并分析双视场光学系统的特点；其次，对比常规的光阑位置固定方案与光阑位置切换方案，得出后者在实现光学总长、最大通光孔径、变焦行程有效压缩的同时，可以实现更大的相对孔径和更好的像质；最终，选用光阑位置切换方案设计了由11片透镜构成，光学总长为150 mm，最大通光孔径为Φ42 mm，变焦行程为35.97 mm的紧凑型双视场可见光镜头。该镜头短焦焦距为32 mm，F数为2.3，满足水平视场角不小于12°、探测距离不小于5 km的要求；长焦焦距为126 mm，F数为3，满足水平视场角不小于3°、畸变小于0.5%、识别距离不小于5 km的要求。设计结果表明，对于焦距32 mm和焦距126 mm，全视场调制传递函数（MTF ）均大于0.45，全视场点列图的均方根 （RMS）直径小于或接近4 μm，整体像质良好。公差分析结果表明，在135 cycles/mm处，全视场MTF大于0.3的概率达到90%以上。

Design of compact dual-field lens for visible light

To make observing and sighting system realize detecting and recognizing function with simple and compact structure, optical compensation method is selected to design compact dual-field lens working at visible light. Firstly, camera was selected and focal length was calculated according to specifications of filed angle and operating range, F number was calculated according to pixel size and minimal illumination of the selected camera, the characters of dual-field optical system were analyzed. Secondly, conventional fixed stop position scheme and switchable stop position scheme were compared, it was concluded that the latter realized total optical length, maximal effective aperture, zoom stroke compressed and larger relative aperture, better image quality. Finally, compact dual-field lens working at visible light composed of 11 lenses, with total optical length 150 mm, maximal effective aperture Φ42 mm, zoom stroke 35.97 mm was designed by switchable stop position scheme. The lens’s parameters were: short focal length was 32 mm, F number was 2.3, met the requirements that horizontal field angle was larger than 12° and detecting range was farther than 5 km; long focal length was 126 mm, F number was 3, met the requirements that horizontal field angle was larger than 3°, distortion was less than 0.5%, and recognizing range was farther than 5 km. Designing results show that for short focal length 32 mm and long focal length 126 mm, MTF curves of all fields get higher than 0.45, RMS spot diagrams of all fields are less than or close to 4 μm, image quality is good enough. Tolerance analysis showed, at 135 cycles/mm, the probability that MTF curves of all fields were higher than 0.3 was 90% above.