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Paper: The Maria Mitchell Observatory and its Digitized Plate Collection
Volume: 410, Preserving Astronomy's Photographic Legacy
Page: 96
Authors: Strelnitski, V.
Abstract: The Maria Mitchell Observatory (MMO), located on Nantucket Island, possesses a collection of over 8,000 wide-field (13° x 16°) photographic plates obtained with the MMO 7.5-inch (19-cm) Cooke/Clark camera, from 1913 to 1995. The collection is relatively rich for three areas of the sky in Scutum, Cygnus and Sagittarius. The catalog of the plates is available online. In 2000- 2002, all the plates were digitized with an AgfaScan T5000 commercial scanner, using both low (840 dpi) and high (2,500 dpi) resolution and the 8 bit gray scale resolution. The image files are stored on CDs and on hard drive RAID-protected storage devices, and copies (on CDs or DVDs) are available on order. Comparison of the images scanned with the AgfaScan T5000 and those scanned with the STScI high-precision GAMMA laser densitometer reveals a characteristic additional noise of up to ≈0.05 mag on the AgfaScan T5000 scans. It is considerably lower than the typical uncertainty of ±0.1-0.2 mag for stellar photometry on the original MMO plates. Several successful projects using the scanned copies of the plates confirm the adequacy of the copies for stellar photometry. Considering that the high-resolution scanning on AgfaScan T5000 was eight times faster than that with the GAMMA, we conclude that scanning the plates of this quality with a commercial scanner of the AgfaScan T5000 class is a reasonable compromise between the quality and the time and cost of scanning.
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