Left panel. Color–magnitude diagram (m_F606W − m_F814W,m_F814W) for all the stars in the Anderson et al. (2008) master list; the 5078 sources selected in this work lie between the saturation limit at m_F814W ≃ 19 and the faint limit m_F814W ≃ 26.5 (dash-dot lines). The red line is the isochrone by Dotter et al. (2007) employed in Richer et al. (2008). The dotted line marks the loci occupied by equal-mass MS-MS binaries. Right panel. The rms for light curves in our sample as a function of the instrumental magnitude. Red circles: median rms averaged over 0.5 mag bins, without any correction. Cyan circles: the same, after PSF-ZP correction. Green circles: both PSF-ZP and dither-ZP corrections applied. Small points are the rms of the individual light curves after both corrections. The solid orange line is the expected theoretical noise level. The superimposed histogram represents the number of targets in each 0.5 mag bin (scale at the right).