  A Lagrangian derivation of the Equation of Motion (EOM) for static
spherically symmetric metrics in F(R) modified gravity is presented. For a
large class of metrics, our approach permits to reduce the EOM to a single
equation and we show how it is possible to construct exact solutions in
$F(R)$-gravity. All known exact solutions are recovered. We also exibit a new
non trivial solution with non constant Ricci scalar.
