  The color-magnitude diagrams of the open clusters NGC 2420 and NGC 2506 have
been investigated as intermediate links between the solar neighborhood and the
Magellanic Clouds. Two sets of theoretical isochrones which include convective
overshoot are zeroed to the sun at solar abundance and to the unevolved main
sequence dwarfs of the Hipparcos catalog at [Fe/H] = -0.4, requiring a
differential of 0.4 mag between the unevolved main sequences at a given color.
Adopting E(B-V) = 0.04 and [Fe/H] = -0.39 for NGC 2506 and 0.04 and -0.29 for
NGC 2420,the respective apparent moduli are 12.70 and 12.15, while the ages of
both clusters are approximately 1.9 +/- 0.2 or 2.2 +/- 0.2 Gyr, depending on
the choice of isochrones. From the composite giant branch of the two clusters,
the mean clump magnitudes in V and I are found to be 0.47 and -0.48
(-0.17,+0.14). Applying a metallicity correction to the M_I values, the cluster
sample of Udalski (1998) leads to (m-M)_0 = 18.42 (+0.17,--0.15) and 18.91
(+0.18,--0.16) for the LMC and SMC, respectively. A caveat to this discussion
and to the claim that clusters of the same abundance and age are identical is
the observation that the (V-I) colors of the red giants in NGC 2506 are
significantly redder at a given (B-V) than the giants in clusters of comparable
age and/or metallicity. If the CCD photometry for NGC 2506 is tied to the
standard system rather than using a general cluster relation between (B-V) and
(V-I), the M_I for the clump will decrease by 0.1 mag.
