I am interested in gravitational lensing caused by a cluster of galaxies (say it has a diameter of 1 Mpc and mass of $10^{12}$ solar masses). How close must a light travel as it passes by to be notably bent - if compared to a case where there would be much smaller object in a spot where is now a center of cluster, like one isolated galaxy?
I am trying to determine angle of deflection for a special case of gravitational potential and I have no feeling for the distances at which lens still has an effect on light.