Aplanatic corrector designs for the extremely large telescope

The next century is knocking on our door, bringing with it the possibility of telescopes even bigger than the 8-10-m-class instruments that have proli ferated over the past decade. The fixed spherical reflector is the most eco nomical and pragmatic way to construct an extremely large primary mirror (3 0-50 m in diameter). Although spherical mirrors have virtues such as manufa cturability and identically figured segments, they also create great amount s of spherical aberration and coma. Here we show that there are several cat optric (all-reflecting) corrector designs that enable a fast telescope base d on a spherical primary mirror. (C) 2000 Optical Society of America OCIS c odes: 110.6770, 350.1260, 110.0110.