A happy conclusion to the SALT image quality saga

Lisa A. Crause; Darragh E. O'Donoghue; James E. O'Connor; Francois Strumpfer; Ockert J. Strydom; Craig Sass; Charl A. du Plessis; Eben Wiid; Jonathan Love; Janus D. Brink; Martin Wilkinson; Chris Coetzee

doi:10.1117/12.924997

17 September 2012 A happy conclusion to the SALT image quality saga

Lisa A. Crause, Darragh E. O'Donoghue, James E. O'Connor, Francois Strumpfer, Ockert J. Strydom, Craig Sass, Charl A. du Plessis, Eben Wiid, Jonathan Love, Janus D. Brink, Martin Wilkinson, Chris Coetzee

Author Affiliations +

Proceedings Volume 8444, Ground-based and Airborne Telescopes IV; 84444I (2012) https://doi.org/10.1117/12.924997
Event: SPIE Astronomical Telescopes + Instrumentation, 2012, Amsterdam, Netherlands

Abstract

Images obtained with the Southern African Large Telescope (SALT) during its commissioning phase showed degradation due to a large focus gradient and a variety of other optical aberrations. An extensive forensic investigation eventually traced the problem to the mechanical interface between the telescope and the secondary optics that form the Spherical Aberration Corrector (SAC). The SAC was brought down from the telescope in 2009 April, the problematic interface was replaced and the four corrector mirrors were optically tested and re-aligned. The surface figures of the SAC mirrors were confirmed to be within specification and a full system test following the re-alignment process yielded a RMS wavefront error of just 0.15 waves. The SAC was re-installed on the tracker in 2010 August and aligned with respect to the payload and primary mirror. Subsequent on-sky tests produced alarming results which were due to spurious signals being sent to the tracker by the auto-collimator, the instrument responsible for controlling the attitude of the SAC with respect to the primary mirror. Once this minor issue was resolved, we obtained uniform 1.1 arcsecond star images over the full 10 arcminute field of view of the telescope.

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Lisa A. Crause, Darragh E. O'Donoghue, James E. O'Connor, Francois Strumpfer, Ockert J. Strydom, Craig Sass, Charl A. du Plessis, Eben Wiid, Jonathan Love, Janus D. Brink, Martin Wilkinson, and Chris Coetzee "A happy conclusion to the SALT image quality saga", Proc. SPIE 8444, Ground-based and Airborne Telescopes IV, 84444I (17 September 2012); https://doi.org/10.1117/12.924997

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