WIYN telescope active optics system

In this paper we describe the active optics system of the WIYN 3.5 meter telescope put into operation in the spring of 1995 on Kitt Peak, Arizona. The active optics system provides real time collimation of the telescope and optical figure control of the primary mirror. The individual subsystems are first described. These include the wavefront curvature sensing technique, the support and articulation of the secondary mirror, the control of the primary mirror figure and rigid body motion, and the mechanics and electronics used for controlling and monitoring the optics. Algorithms for the complete loop are then discussed. This involves mapping coma terms used to actively correct the collimation, while residual phase errors are corrected by active control of the forces supporting the primary mirror. In the next section we compare two operational modes: open loop using mapped collimation and optical figure corrections, and closed loop using feedback from the wavefront sensor directly. Finally, preliminary stellar images obtained with the actively controlled telescope are presented.