Observed PNLF for the PNe sources found in all the ETGs listed in Table 1. The entire central PNLF is fitted to derive the best distance modulus while accounting for the incompleteness of our observations. The corresponding best-fit model is shown by the dot-dashed blue line, with corresponding confidence intervals, whereas the original model PNLF - (from Ciardullo et al. 1989a) is shown by the filled blue line. Blue bars show central PNe, red bars indicate disk (or middle) PNe, and green bars show halo PNe. The green dot-dashed lines show the PNLF model at the best-fit distance modulus, corrected for incompleteness according to the depth of the halo pointing and re-scale to match its integral to the observed number of PNe in this pointing.