Top left panel: K_s vs. (J − K_s) CMD for a less crowded bulge field (a section of tile b204) comparing the 5σ magnitude limit of the CASU aperture photometry with PSF photometry (also with 5σ magnitude limit). The bottom left panel shows histograms for all sources (dashed line) and only the stellar objects (solid line) found in tile b204, also in comparison with the PSF photometry. The right-hand panels show the same analysis for a highly crowded field close to the Galactic Centre (tile b305).