Field Correctors for Large Telescopes

The aberrations of large telescope mirrors can be corrected by lens systems located near to the focal plane. The three-element systems, designed by Ross for the 200-in. (5-m) Mount Palomar telescope, are shown to be amenable to a higher degree of aberration correction, and designs of this form are given, adapted for use at the focus of the primary mirror of a Ritchey–Chrétien telescope. A different form of three-component system gives still better aberration correction, and examples of this are given, suitable for use on the Kitt Peak projected 150-in. (3.8-m) f/2.8 telescope. Simple two-element systems to correct the field aberrations at the focus of the two-mirror Ritchey–Chrétien telescope are also described.