Harvard-Smithsonian Center for Astrophysics
Scanning the Harvard University Plate Stacks

Testing Scanners

There are 400,000 glass photographic plates in the Harvard Plate stacks, exposed in both the northern and southern hemispheres between 1885 and 1989. This 100 year coverage is a unique resource for studying temporal variations in the universe. Because there are so many plates, we are planning to use commercial flatbed scanners instead of the traditional scanning microdensitometer.

During the winter of 2001-2002, before starting our trial run of 100 8-inch by 10-inch plates during the summer of 2002, we tested two high-end flatbed scanners to see whether there was even a chance that they would have enough information to get accurate photometry and astrometry for the stars they contain.

Here are the results of our tests:

After buying a UMAX and a Macintosh computer to run it, we started scanning 8-inch by 10-inch plates during the summer of 2002. We have scanned over 100 plates in a trial to see whether the scanned images have enough information to get accurate photometry and astrometry for the stars they contain. Many of these MC plates are accessible online through the plate catalog search (Hint: search on "M44" and click on "scanned plate"). Bad pixels started to appear in images scanned by the UMAX scanner after our first 100 scans, and we and UMAX were unable to get this now-discontinued model to work as well as it did at first.

M44 Test Project

We tested the photometric and astrometric accuracy of the scanner by looking at M44 over time.

Here are images of a couple of samples. FITS images of 39 of our M44 MC-series plates are accessible online through the plate catalog search (Hint: search on "M44" and click on "scanned plate").