Gravitational potential of galaxy cluster is given as
h00=a√1+(rr0)2
and conditions are such that we can determine: a=2GMc2r0,r0=1√3Mpc. M is mass of cluster.
When r>>r0, potential becomes that of a point mass h00→2GMc2r, so I tried to use derivation for that but I'm not sure it is the right way and calculations quickly become very complicated for given potential.
So my question is: how can I calculate angle of deflection of photon moving at a distance d from cluster in case of such potential ?