Context : Galactic open clusters are since long recognized as one of the best tools for investigating the radial distribution of iron and other metals .

Aims : We employed FLAMES at VLT to collect UVES spectra of bright giant stars in a large sample of open clusters , spanning a wide range of Galactocentric distances , ages , and metallicities .
We present here the results for four clusters : Berkeley 20 and Berkeley 29 , the two most distant clusters in the sample ; Collinder 261 , the oldest and the one with the minimum Galactocentric distance ; Melotte 66 .

Methods : Equivalent width analysis was carried out using the spectral code MOOG and Kurucz model atmospheres to derive abundances of Fe , Al , Mg , Si , Ca , Ti , Cr , Ni , Ba ; non-LTE Na abundances were derived by direct line-profile fitting .

Results : We obtain subsolar metallicities for the two anticenter clusters Be 20 ( [ Fe/H ] = - 0.30 , rms=0.02 ) and Be 29 ( [ Fe/H ] = - 0.31 , rms=0.03 ) , and for Mel 66 ( [ Fe/H ] = - 0.33 , rms=0.03 ) , located in the third Galactic quadrant , while Cr 261 , located toward the Galactic center , has higher metallicity ( [ Fe/H ] =+0.13 , rms=0.05 dex ) .
The \alpha -elements Si , Ca and Ti , and the Fe-peak elements Cr and Ni are in general close to solar ; the s-process element Ba is enhanced .
Non-LTE computations of Na abundances indicate solar scaled values , suggesting that the enhancement in Na previously determined in giants in open clusters could be due to neglected non-LTE effects .

Conclusions : Our results support the presence of a steep negative slope of the Fe radial gradient up to about 10–11 kpc from the Galactic center , while in the outer disk the [ Fe/H ] distribution seems flat .
All the elemental ratios measured are in very good agreement with those found for disk stars of similar metallicity and no trend with Galactocentric distance seems to be present .