Comparison between 4 m and 0.9 m photometry for the central Sculptor pointing for PSF (left) and aperture (right) magnitudes. A plume of short period RR Lyrae variable stars is visible in all bands in the PSF data at B ~ 20.5 − 21; V ~ 20 − 20.5; I ~ 19.5 − 20.5. Solid black errorbars overplotted in the left-hand figures indicate the average error on the magnitude difference at the corresponding magnitude. The residuals of the PSF magnitudes are consistently smaller than the error on the magnitude difference, while for the aperture magnitudes the residuals are similar to the error.