Exploration of a 14-Meter, 1.5-Degree Field of View, Quad-Mirror Anastigmatic Telescope Concept for Wide-Field Spectroscopy and Imaging

Three mirror anastigmatic telescope designs offer excellent imaging performance in a compact optical structure. The introduction of a fourth, fold mirror allows straightforward access to the image surface of the telescope at a Nasmyth position where instrumentation can be located and easily exchanged. The design presented here is of a 14-meter diameter primary providing a 1.5 square degree field of view with an f/4 focus to a pupilcentric image surface. Two fused silica lenses serve as an atmospheric dispersion compensator, a third field lens forms a large radius pupilcentric image. The optical design gives polychromatic (360-1800 nm) encircled energy diameters (EED) of greater than 80% within 0.25 arc-second diameters across the full field at Zenith. Excellent monochromatic image performance extends through and redward of the K-band (2320 nm). The flat fold mirror, located at a pupil, could be upgraded to an adaptive mirror for image correction and/or GLAO. Image performance is given. We believe that this design offers a very powerful, versatile, and scientifically viable facility suitable for the next generation of ground-based facilities for fiber spectroscopy (similar to 18,000 probes), multi-slit spectroscopy, IFU spectroscopy, and imaging.