Left: PNLF of the completeness-corrected PN sample (without accounting for contamination by Ly-α-emitting background galaxies). The error bars along the y-axis account for the Poissonian error and the x-errors for the bin width. The solid blue line shows the analytical PNLF at a distance modulus μ = 31.3 with c₂ = 0.307 (Ciardullo et al. 1989). The solid grey line shows the Ly-α LF (G07) and its variance due to density fluctuations is represented by the shaded region. Right: PNLF of the completeness-corrected PN sample after statistical subtraction of the estimated Ly-α LF. The grey region denotes the magnitude range in which the PNLF might be affected by incompleteness that could not be corrected for. The error bars along the y-axis account for the Poissonian error and the x-errors for the bin width. The solid red line shows the fit of the generalised PNLF, with the best-fit parameters c₂ = 0.69 ± 0.12 and μ = 31.29 ± 0.05. The dotted line shows the fit to the PNLF for c₂ = 0.307 (Ciardullo et al. 1989).