Comparison of photometric redshifts as derived from eight-band ground-based optical/NIR imaging and spectroscopic redshifts for those objects with secure spectroscopic redshifts (see Sect. 2.1). In the bottom panel Δz ≡ (z_spec − z_phot). Members of the Cl J0227-0421 protostructure (see Sect. 3.1) with secure spectroscopic redshifts are denoted in both panels by red diamonds, those with less secure spectroscopic redshifts are shown as blue Xs. For an discussion of the relevance of this comparison for this study and an explanation of the parabolic feature seen in the bottom panel see the text at the end of Sect. 2.3.