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Alignment of the optical systems for the 2.16-m astronomical telescope

The largest astronomical telescope in China with 2 (DOT) 16 m aperture had been installed in 1989 at Xinglong station of Beijing Astronomical Observatory (BAO). From observations of many years including international cooperation programs, a lot of valuable astronomical data and some influential achievement had been obtained. This equipment had been appraised in December 1996. The optics of the telescope has some distinctive features. It has the Ritchey-Chretien Cassegrain system of focal ratiof/9, and the Coud'e system of focal ratiof/45. In this paper, the principle and procedure of alignment of Cassegrain and Coud'e optical systems are described. In the process of adjusting we used two sets of micro-alignment telescope (MAT) and its accessories, designed and manufactured an especially cube prism and its mechanical device. We also used a telescope tube of a 6' theodolite and some adjustable reticles to finish the alignment. With a star as the light source, Foucault's knife-edge test photograph of the optical system at the Cassegrain focus is given. After assembling the fused quartz field corrector on Cassegrain focus, a star cluster photograph, with a whole field of view (30 X 30 cm) also performed. Finally, in the whole field of view from center to edge and corner, the images are round. A member of the appraisement committee measured the linear size. The diameters of dim stars are 0 (DOT) 18 - 0 (DOT) 20 mm. These show that the alignment of the optical system, the design of the fused quartz field corrector, the select of the fused quartz material and its fabricate method are successful.