基于复合式变焦系统结构, 提出了一种三组元连续变焦设计数学模型.在该模型的指导下, 针对中波制冷型15 μm、640×512的凝视型焦平面探测器, 设计了一款紧凑型高变倍比连续变焦光学系统.该系统工作波段为3.7~4.8 μm, F数为4, 利用该模型分配光焦度、计算初始点得到系统焦距变化范围为9~740 mm, 变倍比达80×.整个光学系统仅采用硅、锗两种红外材料, 共八片透镜, 利用二次成像方法及45°反射镜对系统进行了U型折叠, 在实现100%冷屏效率的同时有效控制了横向和纵向尺寸.完成了各动组凸轮曲线的优化设计和对比分析, 从光学传递函数、点列图、畸变、冷反射及环境适应特性等多方面对系统进行了分析.结果表明, 该系统具有变焦轨迹平滑、冷反射抑制特性优良、成像质量佳、环境适应性好及工程可实现性等优点.该数学模型的正确性和可行性也得到了验证.

Based on the structure of compounding zoom system, a mathematical model of three component continuous zoon design was proposed. Under the guidance of the model, a compact high zoom ratio continuous zoom optical was designed with medium-wave cooling 15μm, 640×512 staring focal plane array. The system works in the range of 3.7~4.8μm and F number is 4. By using this model to distribute the optical power, the initial focal point is calculated to obtain the focal length range of 9~740mm and the zoom ratio is 80×. The whole system used only two kinds of infrared materials of silicon and germanium and eight lenses were used. The system was U-folded by using the secondary imaging and two 45° reflecting mirrors, it effectively achieved 100% cold shield efficiency and controlled the horizontal and vertical dimension. It got the moving lens zoom track and cam curve of each group, and analyzed the continuous zoom optical system from MTF, spot diagram, distortion, narcissus, environment analysis and so on. The design results prove that the zoom system has the advantages of smooth zoom track, great narcissus controlled features and excellent image and it has also been found to apply to infrared imaging system matching with advanced middle wave detector greatly. Finally, the correctness and feasibility of the mathematical model are verified exactly.