For our candidates, log (r_eff)−M relation in the V band (red squares), all known dwarfs of the Centaurus group in the surveyed area for which photometry was possible (gray filled squares), Local Group dwarf galaxies (gray dots;  McConnachie 2012) and the candidates from MJB15 (black squares). Also plotted are conservative error bars of 0.5 mag for M_V and 0.05 for log (r_eff). Absolute magnitudes are based on a mean distance of 4.5 Mpc to all Centaurus galaxy candidates. The solid curve represents the completeness limit of the survey. It suggests that most low surface brightness galaxies larger than 26′′ in diameter at the isophotal magnitude of 28 mag arcsec^-2 were detected (for more details see text).