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23 June 2006 Imaging performance of the Hobby-Eberly Telescope
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The HET is a modified Arecibo-style telescope with a segmented spherical primary and a four-mirror spherical aberration corrector (SAC). Objects are tracked by driving the SAC along the focal sphere of the primary. In the original design of the telescope the alignment of the SAC was to be maintained passively. In practice, this could not be done to specifications, leading to degraded imaging quality. We have developed a metrology system to actively control the alignment of the SAC. An autocollimator maintains the optical axis of the SAC normal to the primary mirror beneath it. An absolute distance measuring interferometer (DMI) monitors the SAC/primary mirror distance, maintaining focus. Both systems work at a wavelength of 1.5 microns, well above the operating wavelength of current or planned science instruments and therefore do not interfere with observations. The performance of the system is measured via Hartmann testing. Several upgrades are implemented in the primary mirror control system, including calibration of individual edge sensors, new control system software, and a new method of setting and controlling the overall radius of curvature of the primary array. New techniques were developed to efficiently piston the segments onto the proper sphere radius.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Povilas Palunas, Phillip J. MacQueen, John A. Booth, Robert Calder, James R. Fowler, Matthew D. Shetrone, Stephen C. Odewahn, Pedro Segura, Gordon L. Wesley, George Damm, Jerry Martin, and P. Samuel Odoms "Imaging performance of the Hobby-Eberly Telescope", Proc. SPIE 6267, Ground-based and Airborne Telescopes, 62673V (23 June 2006);

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