Optical design method of a three-mirror anastigmatic telescope with low misalignment sensitivity based on the nodal aberration theory.

We propose a design method for a three-mirror anastigmatic telescope with low misalignment sensitivity and deduce the analytic expression between the misalignment aberration and its optical parameters based on the nodal aberration theory. We establish an optical system as-built performance evaluation model. Using this model as the system's as-built performance evaluation indicator, we can get an optical system that could have both low misalignment sensitivity and good image quality after optimization. The design results of a field bias three-mirror anastigmatic telescope show that the misalignment aberration of the system can be reduced by changing the spacing of the mirrors. When the spacing between the primary mirror and the secondary mirror increases and the spacing from the secondary mirror to the third mirror and the third mirror to the image plane decreases, the misalignment sensitivity will drop significantly. If the mirror spacing is changed by 10%, the misalignment sensitivity of the telescope optimized by our method is only about 85% of that of the traditional method.