改进的离轴三反光学系统的设计

Design of improved off-axial TMA optical systems

基于离轴三反光学系统(TMA)的一般设计方法,总结了设计要点。以两个基于三反光学系统的设计为实例,阐述了通过合理地安排光学结构、将次镜设计为球面反射镜、主镜和三镜在球面基础上改变高次非球面系数等,可使离轴三反光学系统的设计结果接近衍射极限,传递函数在50lp/mm时都接近0.6,Strehl率由通常的0.91提高到0.93。与传统离轴三反系统相比,相机加工公差和面形加工公差从原来的λ/50放宽到λ/40,主、次、三镜的装调公差放宽了4倍。文中的设计降低了相机的加工及装调难度,有助于系统光学特性实现衍射极限,为三反光学系统的广泛应用提供了借鉴和实用参考。

The key design of off-axial Three-mirror Anastigmat（TMA） systems was summarized,and an improved design of the off-axial TMA optical systems was proposed with a new optical structure.By taking two designed systems for examples,the optical elements of the TMA system were reasonably arranged,the secondary mirror was designed as a spherical surface,and the primary and the third mirrors were optimized with high-order aspheric coefficients.Obtained results show that the Modulation Transform Function（MTF） curve of the designed system approaches to the optical diffraction limit with an improved value of 0.6 at the spatial frequency of 50 pl/mm.Compared with the common off-axial TMA optical system,the Strehl ratio can be increased from 0.91 to 0.93.The surface tolerance is relaxed from λ/50 to λ/40,and the assembling tolerances of the primary mirror,second mirror and the third mirror can be relaxed by a factor of 4.The improved design makes the manufacture and assembly of the off-axial TMA optical system much easier,and helps the system to achieve excellent performance in the level of optical diffraction limit.These are beneficial to the popularization of off-axial TMA optical systems.