  We present a BVI photometric study of four old open clusters (OCs) in the
Milky Way Galaxy, Czernik 30, Berkeley 34, Berkeley 75, and Berkeley 76 using
the observation data obtained with the SMARTS 1.0 m telescope at the CTIO,
Chile. These four OCs are located at the anti-Galactocentric direction and in
the Galactic plane. We determine the fundamental physical parameters for the
four OCs, such as age, metallicity, distance modulus, and color excess, using
red clump and PARSEC isochrone fitting methods after finding center and size of
the four OCs. These four old OCs are 2-3 Gyr old and 6 - 8 kpc away from the
Sun. The metallicity ([Fe/H]) values of the four OCs are between -0.6 and 0.0
dex. We combine data for these four OCs with those for old OCs from five
literatures resulting in 236 objects to investigate Galactic radial metallicity
distribution. The gradient of a single linear fit for this Galactocentric
[Fe/H] distribution is -0.052 +/- 0.004 dex/kpc. If we assume the existence of
a discontinuity in this radial metallicity distribution, the gradient at
Galactocentric radius < 12 kpc is -0.070 +/- 0.006 dex/kpc, while that at the
outer part is -0.016 +/- 0.010 which is flatter than that of the inner part.
Although there are not many sample clusters at the outer part, the broken
linear fit seems to better follow the observation data.
