卡塞格林系统是望远系统中最经典的反射式光学系统。常规的卡塞格林系统成像点在系统以外，可以直接采用干涉仪检验。而改良型卡塞格林系统成像点在两镜之间，无法用常规方法进行检验。基于系统特性，主要分为两步检测：对主镜进行精确检验；通过检验系统的弥散斑评价成像质量。在采用轮廓仪测量、阴影法检验以及Zygo干涉仪检测的基础上，通过搭建特殊结构对系统进行精确检测。同时，在检验过程中要边测量边修正面形，使得系统成像质量符合使用要求。

Cassegrain system is the most classic reflective optical system in telescope systems. The imaging point of a regular Cassegrain system is outside the system and thus can be tested using an interferometer. However, the imaging point of the improved Cassegrain system lies between two mirrors, so that it cannot be directly measured. It can be tested in two steps based on the system characteristics: an accurate test is made for the primary mirror; the image quality is evaluated based on the system′s dispersion spot. Such a system is measured by a profilometer and tested by Zygo interferometer and the optical shadow method. A special structure is used to test accurately. The surface figure should be modified based on the measured results in the test process to meet the requirements on the optical system′s imaging quality.