Distribution of [Fe/H] for stars in NGC 6528. a) The black line shows the cummulative distribution of [Fe/H] for the full sample (21 stars). The orange-red line shows the distribution for stars where we have fitted the wings of Halpha to determine T_eff (Method 2), while the purple line shows the distribution for the stars when we have used excitation equilibrium to determine T_eff (Modified Method 2). b) The same as in a) but now only for stars with S/N> 35. c) The black line shows the histogram of [Fe/H] for stars in NGC 6528 for all stars with S/N> 35, while the blue line shows the result when the offset between the distributions for stars analysed with Method 2 and Modified Method 2 has been accounted for. d) The cummulative distribution of [Fe/H]. The colours are the same as in c).