Abstract

The efficiency with which a charge-coupled device (CCD) detects photons depends, amongst other factors, on where within a pixel the photon hits. To explore this effect we have made detailed scans across a pixel for a front-illuminated three-phase EEV05-20 CCD using the standard astronomical B, V, R, and I colour filters. Pixel response functions and photometric sensitivity maps are derived from the scan images. Nonlinear charge transfer inefficiency (CTI) effects were observed and corrected for. The resulting images clearly show the intra-pixel sensitivity variations (IPSVs) due to the CCD electrode structure, and its dependence on wavelength. We briefly comment on the implications of IPSVs and CTI for high-precision photometry and astrometry.