Study On Field Rotation Of 1.2m Alt-Az Telescope And Elimination Of Image-Rotation

There is object-image field rotation phenomena during an Alt-azimuth telescope tracking an object, namely, in the same field, other reference stars which deviates the tracked star with a certain angle rotate around the field center. In addition, if the detector is equipped at Alt-az telescope's Cassegrain focus or coude focus, the telescope optics system is composed of many plane reflectors. Principal section of plane mirror has certain relative motion along with the optical system, so its image field rotates too. And the image of the other reference stars in the field of view is an arc around the optical axis center besides the tracked star being located at the optical axis center becomes a point-like image. In order to obtain a stable, good-quality star image, rotation of the field of view must be compensated.In this paper, the field of view rotation of Yunnan Observatory 1.2m alt-az telescope is researched. Firstly, the object field rotation due to alt-az mounting and the rotation quantity are analyzed and studied, and the conclusion that the parallactic angle q change rate can explain the object field rotation angle is drawn, and the object field rotation magnitude caused by Alt-azimuth mounting in spherical coordinates is transformed to the plane rectangular coordinates. A problem that image collected by 1.2m astronomical telescope is rotated due to plane mirrors system with the movement of azimuth and altitude is introduced in brief. The rotation of view filed is analyzed using the method of ray tracing and matrix optics. The accordant variation function relation of object image rotation and the telescope's azimuth angle and zenith angle are given by the two methods respectively. Finally, the field of view rotation magnitude in 1.2m telescope system is obtained. In this paper, two ways of confirming field of view referenced point are also introduced; namely star observation method and laser imaging method. The principle of the former has been simulated and the latter has been proved by experiment, the field of view referenced point error in one pixel approximately.Basing on elimination rotation principle, several kinds of elimination rotation technology commonly used at present are analyzed, and by analysis and comparison, the conclusion that the optics elimination rotation is the most suitable approach for 1.2m alt-az telescope is drawn. Two kinds of optics elimination rotation which is mainly including reflection elimination rotation and refraction elimination rotation are analyzed and calculated, and the result is refraction elimination rotation more suitable for 1.2m alt-az telescope.It is very important to master the posture change as well as confirm the high resolution shape of the space objects in exploration. With eliminating the field of view rotation of Alt-az telescope, we can detect the space objects actually, and it will also improve the ability of detection and surveillance the space objects in our country.