Pixel mask siz es versus the proxy Kepler magnitude for ~ 21 500 targets observed in C3, colour-coded with the distance (in degrees) to the spacecraft bore sight; black crosses (“×”) indicate 4143 targets from the GO proposal 3048, which all relate to extragalactic studies of galaxies or active galactic nuclei (AGN), hence these targets are typically truly extended objects not expected to follow the general trend for stars; the red circular markers give the median mask size for 0.5 wide magnitude bins (not including the extragalactic targets); the full black line shows the mask sizes relation used in Aigrain et al. (2015) (obtained from engineering data); the dashed black line gives the relation from Armstrong et al. (2015).