Left panel: spectroscopic versus photometric redshifts for the 60 cluster fields in this study. Outliers, objects for which , are marked in red. The outlier fraction is less than 3%, the scatter (in ) of the remaining objects is σ_z = 0.035. Right panel: same for the COSMOS field, also using only the ugri-filters. The outlier fraction and scatter are slightly larger as a result of deeper spectroscopic data (in particular at higher redshift where the ugri-filters lose their constraining power).