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Proceedings Paper

A happy conclusion to the SALT image quality saga
Author(s): 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
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Paper 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.

Paper Details

Date Published: 17 September 2012
PDF: 9 pages
Proc. SPIE 8444, Ground-based and Airborne Telescopes IV, 84444I (17 September 2012); doi: 10.1117/12.924997
Show Author Affiliations
Lisa A. Crause, South African Astronomical Observatory (South Africa)
Darragh E. O'Donoghue, Southern African Large Telescope (South Africa)
James E. O'Connor, South African Astronomical Observatory (South Africa)
Francois Strumpfer, South African Astronomical Observatory (South Africa)
Ockert J. Strydom, South African Astronomical Observatory (South Africa)
Craig Sass, South African Astronomical Observatory (South Africa)
Charl A. du Plessis, Southern African Large Telescope (South Africa)
Eben Wiid, Southern African Large Telescope (South Africa)
Jonathan Love, Southern African Large Telescope (South Africa)
Janus D. Brink, South African Astronomical Observatory (South Africa)
Martin Wilkinson, Southern African Large Telescope (South Africa)
Chris Coetzee, Southern African Large Telescope (South Africa)


Published in SPIE Proceedings Vol. 8444:
Ground-based and Airborne Telescopes IV
Larry M. Stepp; Roberto Gilmozzi; Helen J. Hall, Editor(s)

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