[108.03] Optical Design for the 8.4m Large Synoptic Survey Telescope

AAS 205th Meeting, 9-13 January 2005
Session 108 LSST
Poster, Wednesday, January 12, 2005, 9:20am-6:30pm, Exhibit Hall

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[108.03] Optical Design for the 8.4m Large Synoptic Survey Telescope

L. G. Seppala (LLNL), M. Liang, C. F. Claver (NOAO), J. Burge (U. Arizona), K. Cook (LLNL/NOAO), L. Daggert (NOAO), S. Ellis (Photon Inc.), S. M. Kahn (SLAC), V. Krabbendam (NOAO), D. Sweeney (LSST Inc./LLNL), C. Stubbs (Harvard), D. Wittman, J. A. Tyson (UC Davis)

The proposed 8.4m Large Synoptic Survey Telescope (LSST) facility will digitally survey the entire visible sky. It will explore the nature of dark matter and dark energy, open the faint optical transient time window and catalog earth-crossing asteroids >300m in diameter. This concept was strongly endorsed by the three National Academy of Sciences reports: “Connecting Quarks with the Cosmos”, "Astronomy and Astrophysics in the New Millennium" and “New Frontiers in the Solar System”. In response to these endorsements we present the design of a modified 8.4m Paul-Baker or Laux⁽¹⁾ telescope that expands the etendue ("A - Omega") product to >300m²deg², a factor of >50 beyond any existing facility. This evolved telescope design has increased etendue to meet the demanding science requirements for the LSST and simplifications in the optical prescription to enhance manufacturability. The optical design delivers a 3.5-degree diameter field of view (9.62 deg²) with superb <0.2 arcsec FWHM images over 5 spectral bands covering 400-1000 nm. The flat focal surface has a plate scale of 51 microns/arcsec (f/1.25), chosen to match the 10 microns pixel size of a large 0.65m diameter mosaic digital detector. The f/1.14 primary can be made using polishing techniques and metrology methods pioneered at the University of Arizona Mirror Lab for the 8.4m f/1.1 Large Binocular Telescope primaries. The 3.4 m convex secondary is twice the size of the largest convex secondary yet manufactured; the 1.7 m MMT f/5 secondary. We show a fabrication and testing plan for this optic. The corrective camera optics are significantly simplified from earlier designs in that all refractive elements have spherical surfaces. In addition the 3 mirror telescope system delivers, without the camera corrector optics, a spherical wavefront on axis that greatly helps in initial assembly and alignment.

1. R. N. Wilson, ``Reflecting Optical Telescopes I", Springer A&A Library, 2000, Chapter 3.6.5.

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