  In this paper we study long range modifications of gravity in the consistent
framework of bigravity, which introduces a second massive spin-2 field and
allows to continuously interpolate between the regime of General Relativity
(mediated by a massless spin-2 field) and massive gravity (mediated by a
massive spin-2 field). In particular we derive for the first time the equations
for light deflection in this framework and study the effect on the lensing
potential of galaxy clusters. By comparison of kinematic and lensing mass
reconstructions, stringent bounds can be set on the parameter space of the new
spin-2 fields. Furthermore, we investigate galactic rotation curves and the
effect on the observable dark matter abundance within this framework.
