We investigate , on the basis of CCD Strömgren photometry , the ages and metallicities of six LMC clusters together with their surrounding field population .
The clusters and metallicities are : NGC 1651 ( in the range [ Fe / H ] = -0.65 dex to -0.41 dex ) , NGC 1711 ( -0.57 \pm 0.17 dex ) , NGC 1806 ( -0.71 \pm 0.23 dex ) , NGC 2031 ( -0.52 \pm 0.21 dex ) and NGC 2136/37 ( -0.55 \pm 0.23 dex ) and NGC 2257 ( -1.63 \pm 0.21 dex ) .
The metallicities for NGC 1651 , NGC 1711 , NGC 1806 and NGC 2031 have been determined for the first time ( NGC 2031 and NGC 2136/37 are interesting for the Cepheid distance scale ) .

In the cluster surroundings , we found about 650 field stars that were suitable to be used for a determination of an age-metallicity relation ( AMR ) .
Our method is to estimate ages for individual stars on the basis of Strömgren isochrones with individually measured metallicities .
With this method we are able to sample the AMR of the field population up to 8 Gyr .

Our metallicity data are incompatible with models predicting many metal-poor stars ( G-dwarf problem ) .
The metallicity of the field population increased by a factor of six , starting around 2 Gyr ago .
The proposed AMR is consistent with the AMR of the LMC cluster system ( including ESO 121 SC03 and three clusters with an age of 4 Gyr ) .

The proposed AMR is incompatible with the recently proposed AMR by Pagel & Tautvais̆vienė ( [ 1998 ] ) .