  We analyze new, high quality multicolor light curves of four overcontact
binaries: AK Her, HI Dra, V1128 Tau and V2612 Oph, and determine their orbital
and physical parameters using the modeling program of G. Djurasevic and
recently published results of radial velocity studies. The achieved precision
in absolute masses is between 10 and 20%, and in absolute radii between 5 and
10%. All four systems are W UMa type binaries with bright or dark spots
indicative of mass and energy transfer or surface activity. We estimate the
distances and the ages of the systems using the luminosities computed through
our analysis, and perform an O-C study for V1128 Tau, which reveals a complex
period variation that can be interpreted in terms of mass loss/exchange and
either the presence of the third body, or the magnetic activity on one of the
components. We conclude that further observations of these systems are needed
to deepen our understanding of their nature and variability.
