Extremely achromatic f/1.0 all-spherical camera constructed for the high-resolution echelle spectrometer of the Keck telescope.

We present a very large f/1.O prime focus, all-spherical, all-fused-silica catadioptric camera. It contains a two-element airspaced corrector, an f/0.76 primary mirror, and a singlet final element. It accommodates a chromatic range from 0.3 to 1.1µm or more without refocus. It is optimized with an external entrance pupil but can be reoptimized for other pupil distances. In spite of its 30-in. (76.2-cm) focal length, it delivers 12.6-µm (rms) average image diameters to a 3.6-in.- (9.1-cm-) diameter flat focal surface. It is thus well matched to the (7-15µm) pixels and to the size of a (2 × 2) mosaic of today's largest available CCD's.