The Connotation and Measuring Way of the Optical Axis Change of the LLMC

Several elements causing the optical axis change of the LLMC are discoursed in this paper, including optical axis change resulting from different thermal expansion coefficients between optical glass and metal material, the different degree of lightness of fixture of the primary mirror and secondary mirror in the primary mirror cell in different temperature, and the displacement and rotation of the primary and secondary mirrors relative to the primary mirror cell resulting from the different stress directions as the telescope is in different vertical angle.The method to measure the optical axis change is introduced in this paper.There is an optical hole lighted from rear of the micrometer, It serves as a man-made stellar image on the video CCD via the primary mirror, the secondary mirror and the 30mm×40mm self-collimation plane mirror fixed in the tube vertical to the optical axis.The optical axis change in the two perpendicular directions may be gotten by comparing the difference between the two measured coordinates of the man-made stellar image before and after transposition, this procedure solves the problem of real-time determination of the flexure of the tube.