Manufacture and test of Cassegrain system's primary mirror with large relative diameter and lightweight

The Cassegrain system is manufactured with focal length of 6000 mm, and relative diameter of 1/10. The diameter of the primary mirror is 600 mm with its relative diameter of 1/1.2 and the material of the primary mirror is crystallite glass. Because of even holes on the back of the primary mirror, the lightweight ratio of the primary mirror is 50%. For the reason of large relative diameter and light weight the manufacture of the system is difficult. In the course of the manufacture new methods are developed based on the traditional methods. The support of nine points is used based on the support of three points and finally the primary mirror is made with a high precision. The diameter of dispersion circular of the Cassegrain system is less than 0.02 mm, peak value (PV) of Cassegrain system is 1.23λ (λ=0.6328 μm), and the root-mean-square (RMS) value of system is 0.18λ.