2 Observations

The observations were done in the standard Johnson's BV and Cousins' R bands with the $1.05 \, \rm m$ REOSC telescope of the Torino Astronomical Observatory. The instrument is endowed with a $1242\times 1152$ CCD device with a scale of $0.47 \, \rm arcsec$ per pixel. Flat field frames are taken every night and the median is used for image correction. The data are reduced with the Robin procedure locally developed. This includes bias subtraction and flat field correction; a circular gaussian fit is performed after background subtraction through an inclined plane. We made BVR photometry in order to calibrate the source magnitude: Landolt's fields (Landolt 1992) were observed during photometric nights and the BVR magnitudes of a number of reference stars in the fields of the BL Lacs were estimated. The transformation to the standard system was obtained with the Calib procedure written locally. The resulting photometric sequences are published in Villata et al. (1998a).

The coordinates of the observed BL Lacs are given in Table 1.

  

Table 1: List of the observed BL Lacs