USRA and the US Naval Observatory, Washington DC, USA
Abstract. The USNO 8-inch astrograph has been equipped with a Kodak 1536x1024 pixel CCD since June 1995, operating in a 570-650 nm bandpass. With 3-minute exposures well exposed images are obtained in the magnitude range R = 8.5 - 13.5 mag. An astrometric precision of 10 to 15 mas for those stars is estimated from frame-to-frame comparisons. External comparisons reveal an accuracy of about 15 mas for those stars in a 20' field of view. For fainter stars, the error budget is dominated by the S/N ratio, reaching about 100 mas at R=16 under good observing conditions.
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Please look up The Astonomical Journal , 113, 1925 (1997) for a complete version of that paper.