We demonstrate that a wide range of viable f (R) parametrizations (including the Hu and
Sawicki and the Starobinsky models) can be expressed as perturbations deviating from the
Λ CDM Lagrangian. We constrain the deviation parameter b using a combination of
geometrical and dynamical observational probes. In particular, we perform a joint likelihood
analysis of the recent type Ia supernova data, the cosmic microwave background shift
parameters, the baryonic acoustic oscillations and the growth rate data provided by the …