For this work, we selected 23 frames, namely nine for the U-domain, seven for V and seven for R (Table 2). The plates were then calibrated by means of ESO's ETA-wedge spectra (see Paper VII). This gives relative intensities of the night sky (including all the atmospheric and zodiacal light effects). Parallel to these exposures simultaneous, photoelectric measurements were made by one of us (TSK) with the 61 cm Bochum telescope at La Silla, which then were used to determine atmospheric extinctions, colour transformations, zero points of absolute intensities and airglow values for different zenith distances. All plates were digitized using the PDS machine of the Astronomisches Institut der Westfälischen Wilhelms-Universität at Münster. The diaphragm was , corresponding to about in the sky. Special care was taken to reveal possible time-dependent sensitivity changes of the scanning system, which, however, proved to be of excellent stability. The paper strip chart records of the photoelectric measurements were processed by means of a standard digitizer table commercially available for personal computers.