In reply to Jan's question about...
"...Does anyone knows a trick to estimate the magnitudes of stars
that are not in the guide database but on the real sky map?"
I'd suggest using USNO-A2.0 for this purpose. The dataset is
described in some detail, including links for downloading portions
of it from Web servers, at:
http://www.projectpluto.com/datasets.htm#A2
Download a piece of that dataset covering the RS (or DSS image,
or one of your own images imported into Guide), and you'll then be
able to get A2.0 magnitudes for the stars in that area. (Generally,
A2.0 goes down about as faint as the DSS does.)
-- Bill