A Test of Commercial Scanners for Digitization of Astronomical Plates

Digitization of astronomical plates has started in China, and the selection of high-precision scanners is a primary task for the digitization. We have tested 3 scanners, Epson V750 Pro, Epson 10000XL, and Phase One PowerPhase FX⁺. We have found that the PowerPhase FX⁺ has the highest scan precision, with the stability of scanning direction better than 0.5μm which equals to that of the CCD linear-array direction. We use the UCAC3 catalog as the reference in the test. Our results show that the images resulting from the scanning of a PowerPhase FX⁺ have complicated distortions, which need to be corrected with a 3-order plate model. Using such corrections the positional measurement accuracy of stars is 0.1" for the M79 astronomical plate taken with the Sheshan 40cm Telescope of the Shanghai Astronomical Observatory in 1987.