VI photometry of NGC 2157

Construction of a color-magnitude diagram and isochrone fitting yield an age of {tau}=10^8^yr, a reddening E(B-V)=0.1, and a distance modulus of 18.4mag. Our data cover the mass range 0.75M_{sun}_<=m<=5.1M_{sun}_.

We find that the cluster mass function changes significantly from the inner regions to the outer regions, becoming steeper (larger number of low-mass stars relative to high-mass stars) at larger radii. The age of NGC 2157 is comparable to its two-body relaxation timescale only in the cluster core. The observed steepening of the mass function at larger radii is therefore most likely an initial condition of the cluster stars.