OLD OPEN CLUSTERS - THE INTERESTING CASE OF BERKELEY-21

We present CCD BVI photometry of the old open cluster Berkeley 21, one of the most distant clusters in the Galactic anticentre direction, an d possibly the lowest metallicity object in the open clusters sample. Its position and metal abundance make it very important for the study of the Galactic disc. Using the synthetic colour-magnitude diagram met hod, we estimate values for the distance modulus (m - M)(0) = 13.4-13. 6, reddening E(B - V) = 0.74-0.78 (with possible differential absorpti on), and age = 2.2-2.5 Gyr.