Background source population. Left panel: galaxy number counts estimated from the COSMOS i-band catalogue (grey bars), compared with the results of Capak et al. (2007 black line), together with the 5σ HFF and CLASH F814W depth limit (cyan and green vertical lines). Galaxy counts added in the faint end to match the HST deep counts are coloured in magenta. Right panels: redshift distributions for six magnitude bins, p(z|Δm), coloured according to the magnitude bin from which they are extracted (left plot).