Stars in the DE1756−48 field that are used for the astrometric reduction and are included in the catalogue. The UCD is marked with a star, bright stars with magnitudes within ±0.5 mag of the target are shown with solid circles, and open circles show all other reference stars. The footprints of the FORS2 chips and the axes orientations are indicated. Only catalogue stars within 1′50′′around the target are shown, and concentric circles with increasing radii of R_opt(k) mark reference fields used for for the reduction with k = 4,6,8,10,12,14,16. See text for details.