  We show that in the weak field limit the light deflection alone cannot
distinguish between different $R + F[g(\square)R]$ models of gravity, where $F$
and $g$ are arbitrary functions. This does not imply, however, that in all
these theories an observer will see the same deflection angle. Owed to the need
to calibrate the Newton constant, the deflection angle may be model-dependent
after all necessary types of measurements are taken into account.
