Optical design for a 1-degree FOV, 30-meter telescope

We are exploring the feasibility of a very large telescope with a wide field of view for multi-object spectroscopic surveys. This paper presents a brief overview of the scientific need for such a facility, a possible optical design for such a telescope, and a description of how such a telescope might function for both wide-field, seeing-limited spectroscopy and narrow-field, high-Strehl imaging and spectroscopy. The science is primarily driven by the fact that imaging surveys are now capable of cataloguing vast numbers of targets that would take a formidable amount of time on currently existing telescopes for spectroscopic followup. The telescope design, a 4-mirror extension of the Paul concept, is a 30-meter telescope that delivers a full 1 degrees field at f/4 with excellent image performance across the full field. The primary is an f/1, 30-meter. The secondary has a diameter of 5.3-meters and contains a pure conic surface that delivers an uncorrected focus between the primary and secondary. The tertiary mirror is located at the vertex of the primary and has a diameter of about 10.6-meters. The quaternary mirror, located at the position of the initial focus, is about 4.4-meters and images the final focus back at the vertex of the tertiary mirror. The initial design had both the tertiary and quaternary miners with high-order, even aspheric surfaces. Further study has led to a simplification of the design in which the tertiary is now a pure conic like the primary and secondary mirrors, and the quaternary mirror is something like a Schmidt corrector with only modest fourth and sixth order terms.