  Vacuum Brans-Dicke theory can be self-consistently described in two frames,
the Jordan frame (JF) and the conformally rescaled Einstein frame (EF), the
transformations providing an easy passage from one frame to the other at the
level of actions and solutions. Despite this, the conformal frames are
inequivalent describing different geometries. It is shown that the predictions
of the weak field lensing (WFL) observables in the EF are different from those
recently obtained in the JF for the vacuum Brans-Dicke class 1 solution. The
value of the Brans-Dicke coupling parameter $\omega$ from the Cassini
spacecraft experiment reveals the degree of accuracy needed to experimentally
distinguish the WFL measurements including the total magnification factor in
the two frames.

General Relativity and Quantum Cosmology