We report on UBVRI CCD photometry of two overlapping fields in the region of the intermediate-age open cluster NGC 2158 down to V = 21 .
By analyzing Colour-Colour ( CC ) and Colour-Magnitude Diagrams ( CMD ) we infer a reddening E _ { B - V } = 0.55 \pm 0.10 , a distance of 3600 \pm 400 pc , and an age of about 2 Gyr .
Synthetic CMDs performed with these parameters ( but fixing E _ { B - V } = 0.60 and [ { Fe / H } ] = -0.60 ) , and including binaries , field contamination , and photometric errors , allow a good description of the observed CMD .
The elongated shape of the clump of red giants in the CMD is interpreted as resulting from a differential reddening of about \Delta E _ { B - V } = 0.06 across the cluster , in the direction perpendicular to the Galactic plane .
NGC 2158 turns out to be an intermediate-age open cluster with an anomalously low metal content .
The combination of these parameters together with the analysis of the cluster orbit , suggests that the cluster belongs to the old thin disk population .