Nonstandard representations of aspheric surfaces in a telescope design

Space-based telescopes for sub-mm astronomy may require large, segmented primary mirrors. While spherical segments are the easiest to manufacture and test, a fast sphere produces large aberrations which must be corrected by one or more aspheric surfaces. Attention is presently given to an f/10 system with an f/0.7 spherical primary mirror and a field of view of + or - 1.5 min of arc. The third and fourth mirrors are conics, and the secondary is a 24th-degree power series on a base sphere. For sub-mm astronomy, a reasonable target for this design is a diffraction-limited image at 30 microns. In an effort to improve performance, the Wassermann-Wolf (1949) approach to aspheric design was applied.