The spherical aberration corrector of the Southern African Large Telescope (SALT)

The Southern African Large Telescope (SALT) is a 10-m class telescope for optical/infrared astronomy to be sited at Sutherland, the observing station of the South African Astronomical Observatory. This telescope, which is almost fully funded and whose construction has begun at the time of writing, will be based on the principle of the Hobby Eberly Telescope (HET) at McDonald Observatory, Texas: a cost-effective design involving a tilted-Arecibo concept with a segmented spherical primary of diameter 11 metres. A spherical aberration corrector (SAC) mounted on a tracker beam at the prime focus delivers a high quality image to the focal plane and enables a celestial object to be followed for twelve degrees across the sky. The SAC is the subject of this paper: the results from the already published design study will be summarized, and recent work on the system that will be built will be presented.