逐级优化法是根据离轴三反射光学系统结构参数的像差灵敏度系数大小来确定主镜、次镜和第三反射镜的加工次序的。其方法是逐级优化确定各光学零件的加工公差，加工完成后测量光学元件结构参数，代入光学设计软件进行优化，进而确定光学系统的装调公差。采用该方法制定三反射系统的加工装调公差时将加工和设计过程有机的结合起来，在满足设计要求的前提下使系统的加工和装调公差得到最大程度地放松。

Based on the aberration sensitivity of structural parameter of offaxis threemirror anastigmat (TMA), the fabrication sequence of the primary mirror, the secondary mirror and the tertiary mirror is selected. The method is to determine the exact fabrication tolerance of each mirror through the optimization step by step. All three mirrors′ structural parameters are measured after fabrication, and these parameters are used to determine the assembly tolerance through optimization with optic system design software. By taking fabrication, alignment and design process into consideration, the fabrication and assembly tolerances are released to the maximal degree while the system specification is still achieved.