OFF-AXIS SYSTEMS FOR 4-M CLASS TELESCOPES

We describe here an off-axis design for a 4.0-m astronomical telescope . We show that the geometric optical performance of this configuration can equal that of an on-axis conventional configuration while the dif fractive performance fundamentally surpasses conventional telescopes b ecause of the absence of pupil obstruction. The specific optical desig n described here uses a single off-axis primary mirror to obtain three distinct final focus ports: an f/10 port (with corrector) for wide-fi eld imaging and spectroscopy with a field of view (FOV) of 15 arc min; a small-field, 2-reflection f/10 port suitable for polarimetry and co ronagraphy; and a slower, f/16 (3-reflection) port with a 7 arc min FO V. For general astronomical observations requiring high optical throug hput and low scattered light, this design is superior to conventional Ritchey-Chretien optical configurations. (C) 1998 Optical Society of A merica.