The dependence of the oxygen abundance of the NGC 5128 PN sample from the Cloudy photoionization modelling (Table 8) on the observed [O III] 5007 Å luminosity (uncorrected for reddening) from the 5007 Å photometry of Hui et al. (1993b). The dotted line shows the theoretical relation of Dopita et al. (1992) scaled to the brightest PN, while the dashed line shows a second order polynomial fit to all the data points.