S/N per resolution element as a function of i_AB magnitude. Red symbols are the passive sample, green the SF sample, blue the LBG sample, and black the AGN sample. Different symbol shapes indicate the different exposure times: circles for 20-hour, diagonal crosses for 40-hour, and crosses for 80-hour exposures. The dotted line corresponds to S/N = 5 per resolution element, while the dashed line to S/N = 10.