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Hi Ric, I ordered an Epson 4990 for use in an undergraduate astronomy project over the last couple of months. My student used it to scan old photographic plates from an observatory in Italy, and thus to evaluate whether the dynamic range, resolution and astrometric stability made a high end "pro-sumer" flatbed a suitable low-cost means to digitise old but valuable plates like this. Old plates have extremely important uses in long-baseline astrometric and photometric studies. The IAU are still arguing over digitisation standards, because if most plate archives will only be scanned once, and face possible destruction once scanned, they want to make sure that every bit of information is captured. In the meantime, I wanted to see what could be done "on the cheap". Anyway, we astrometrically calibrated the scanned plate against the 2MASS point source catalog, and compared it with a DSS image from the 1950s, which we had also recalibrated using 2MASS. There was not much time for the project, so the student only got most of the way up the long learning curve. Nevertheless our conclusion after some basic tests was that for our data, the plate quality was the limiting factor - not the scanner. This may reassure you... Ray "noting that 'amateur' equipment is now good enough to do some real science" Butler. RThiem@aol.com wrote:
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