The optical design of the Southern African Large Telescope

SALT, although similar to the Hobby-Eberly Telescope (HET - the prototype for a fixed altitude optical analog of the Arecibo radio telescope), has some significant differences in the optical design. This paper gives an overall description of the SALT optics and a description of the analyses done in order to develop an optical error budget, which satisfies the overall requirements for total image quality. An optical prescription for SALT is presented, including an optical model of the telescope with a segmented primary mirror (PM) array. The design of the spherical aberration corrector (SAC) is summarised, with particular reference to the effects of non-axisymmetric distortion. The concepts for an atmospheric dispersion corrector (ADC), and guidance and focusing (GF) systems, are also discussed. Finally, the primary mirror alignment system (PMAS) concept is presented and the difficulty in controlling the Global Radius of Curvature (GRoC) discussed.