A grid of 200 synthetic spectra was built in the wavelength region λλ 478-530 nm, and a method was developed for deriving the stellar parameters temperature, gravity and metallicity from low-resolution stellar spectra. The parameters of the observed spectra are derived by dividing the observed spectrum by that of a reference star. The resulting δf(λ) = log F*/Fref is then used, in conjunction with the grid of synthetic spectra, to derive the final parameters, through a perturbation method. The method was applied to a sample of 41 stars in the Basel field SA 141 (1 = 245°, b = −85.8°). Since this direction points closely to the south galactic pole, the binning of stars into appropriate distance intervals provides a coarse view of the metallicity distributions associated with the major galactic populations: we find the thin disk, thick disk and halo components near the current best estimates of their scale heights above the galactic plane. The first results were presented in Cayrel et al. (1991a, A&A, 247, 108; 1991b, A&A, 247, 122). Further observations are in progress, with the aim of having a sample of about 1000 stars.