The Role of Small Telescopes in Modern Astronomy, October 14-15, 1996, Lowell Observatory

The Eight-Inch CCD Astrograph

Marvin E. Germain (
U.S.Naval Observatory

The USNO Eight-Inch CCD Astrograph is a robotic, refracting telescope currently under development for the purpose of conducting an all-sky, astrometric survey to 16th magnitude with an anticipated mean error of 30 mas. While initially intended for photographic astrometry, the tail piece has been fitted with a 1K by 1.5K CCD camera for test purposes. This will soon be replaced by a 4K by 4K camera, allowing imaging of one square degree. The pixels are 9 microns square, resulting in three pixels across an image when the seeing is one arcsecond. A 4.5- magnitude diffraction grating has been installed at the entrance pupil, giving the system a dynamic range of about 10.0 magnitudes. This telescope features a fully-automated mount. The dome, an X-Y slide, and the focus are also set automatically. The X-Y slide, which is attached to a separate guide scope, allows guiding on stars at any position in the field. Guiding is done with an SBIG ST-4 autoguider. The system is controlled from a PC via an embedded single-board computer. It has an advanced, red- corrected lens developed in the University of Arizona Optical Sciences Department achieving nearly diffraction-limited imaging over a nine-degree flat field.

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