依据近轴光学理论求解双焦系统初始结构

为了快速得到双焦光学系统初始结构，依据近轴光学理论设计一款双焦、双视场光学系统。通过高斯光学理论及物像交换原则求解光学系统近轴光学元件的初始位置，分组将标准透镜插入到求解位置上，通过逐步增大近轴元件的焦距优化镜组及镜片间隔，使插入的透镜组焦距趋向该近轴元件焦距的理论计算值。以此类推完成每个镜组的优化设计。通过该方法设计了焦距为40/120 mm、视场为8.6°/2.9°的光学系统，所有镜片均为球面。在奈奎斯特频率100 lp/mm处，120 mm焦距时调制传递函数为0.58，接近衍射极限；40 mm焦距时调制传递函数为0.52。设计结果表明该方法适用于双视场光学系统，可快速得到光学系统初始结构，简化了设计难度。

Solving initial structure of bifocal system according to theory of paraxial optics

In order to get the initial structure of the bifocal optical system quickly, a bifocal and dual-field optical system was designed according to the theory of paraxial optics. The initial position of the optical elements near the axis of the optical system was solved by Gauss optics theory and the principle of object and image exchange. The standard lens was inserted into the solution position by grouping. The lens spacing was optimized by gradually increasing the focal length of the elements near the axis, so that the focal length of the inserted lens set approached the theoretical calculated value of the focal length of the element near the axis. Then the method was used to completes the optimal design of each lens set. An optical system with a focal length of 40/120 mm and a field of view of 8.6°/2.9° was designed by this method. All the lenses were spherical. At Nyquist frequency of 100 lp/mm, the modulation transfer function at 120 mm focal length was 0.55, close to the diffraction limit. The modulation transfer function at a focal length of 40 mm was 0.4. The design results show that this method is suitable for dual-field optical system, and the initial structure of optical system can be obtained quickly, which greatly reduces the difficulty of design.