In this paper we consider the approximation of bivariate functions by using the well-established filtered back projection (FBP) formula from computerized tomography. We establish error estimates and convergence rates for the FBP reconstruction method for target functions f from a Sobolev space H α (ℝ 2 ) of fractional order α > 0, where we bound the FBP reconstruction error with respect to the weaker norms of the Sobolev spaces H σ (ℝ 2 ), for 0 ≤ σ ≤ α. By only assuming Hölder continuity of the low-pass filter's window function, the results of this paper generalize previous of our findings in [2]-[4].