Accurate astrometric and photometric calibrations of all-sky photographic
surveys, such as the Palomar Quick-V survey and the UK SERC-J survey, digitised
for the construction of the Hubble Space Telescope Guide Star Catalog, are of
extreme astrophysical value. Their wide range of applications includes, for
example, galactic structure, stellar populations, extragalactic studies, and deep
sky catalogs for mission planning and telescope operations. The Guide Star
Photometric Catalog (GSPC-I, Lasker et al. 1988) provides stellar calibration
sequences, placed approximately in the center of each survey plate, with a
limiting magnitude of V = 15 mag. The goal of our program is to extend these
calibrators to V = 20 mag in the Johnson-Kron-Cousins B, V and R passbands, with
an accuracy of 0.05 mag. This is accomplished by taking CCD frames centered on the
faintest star of each GSPC-I sequence. Typically, both long and short exposures
are acquired in each field in order to link the bright and faint ends of the
sequence.