Abstract
Currently, IIIa-J objective-prism plates from the Calar Alto and ESO Schmidt telescopes are used at the Hamburg Observatory to search for and to identify new astronomical objects. Major projects are the Hamburg Quasar Survey, the Hamburg-ESO Survey, and the Hamburg-Munich collaboration to identify sources from the ROSAT All-Sky Survey (cf. contributions to this conference by Hagen et al., Wisotzki, and Voges). The objective-prism plates are digitized with a PDS microphotometer. To determine the brightness of the digitized objects, a method to calibrate the plates was developed, using an internally determined characteristic curve and its external calibration with photometric sequences. Having spectral information, we are able to synthesize the Johnson B-filter as this filter is fully covered by the spectra.
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