Light curves of HD 189733 (top) and RR Lyrae (bottom). For HD 189733 the reduced data (black points) have been folded to the orbital period of HD 189733b and the folded light curve has been binned by 0.005 in phase (red errorbars). The errorbars have been scaled by a factor five for clarity. For RR Lyrae the reduced data has been folded to twice the period of its variability (black points) and the folded light curve has been binned by 0.02 in phase (red line). We note that the scatter away from the red line is primarily caused by residual systematics in the data taken by the zenith camera, which suffers from the strongest vignetting.