Digitization of the FBS plates started in 2002.
After several test scans on a set of plates, all the FBS plates were
carefully cleaned and digitized (the emulsion in contact with the
scanner glass plate) with the scanner Epson Expression 1680 Pro.
in transparency (positive) mode.
An `ad hoc" program, SCANFITS, written by
Stefano Mottola (DLR -
Institute of Planetary Research, Berlin;)
allowed the resulting image to be written directly in FITS format
with corresponding information about the plate in the header.
In order to obtain the zero for a transparency scale, a black paper sheet
was used to cover one of the unexposed plate corners; the higher limit
of the transparency scale was obtained by utilizing one of the clean
unexposed corners. The data numbers (DN) range from 0 (dark) to 16383
(transparent); a 16-bit transparency range was used. In practice,
the black corner counts were around 600 DN and the clear plate counts
14000 DN, thus corresponding to an effective 4.1 density range of
The scanning resolution was 1600 dpi: so the pixel size is about 16
micron. The typical length of an FBS spectrum is 1.7 mm, corresponding to
107 pixels along the wavelength scale.