Redshift distributions resulting from the colour selection for galaxy clusters at redshift 1.2 ≲ z ≲ 1.7 in the HUDF region. The selected source galaxies (solid lines) are mostly at redshift z ≳ 1.7. Removed galaxies (dashed lines) are mostly at redshifts z ≲ 1.7. The distributions only show galaxies matched between the five reference redshift catalogues (R15, R15_fix, R20, S14, and Oe18) and the photometric catalogue from this work. We additionally display the average lensing efficiency curve as a function of redshift (grey dash-dotted line) at the median lens redshift of the clusters at z_l = 1.4. Left: redshift distributions for the five redshift catalogues and employing a colour selection based on the S14 photometry. The uncertainties represent the standard deviations from 50 noise realisations of the U band in the S14 photometry. Right: redshift distributions for the five redshift catalogues and employing a colour selection based on the LAMBDAR photometry measured from our observations of HUDF in U_HIGH and from the S14 stacks in different HST-bands (see text).