I just read this news: http://www.space.com/29042-cosmic-ring-photo-rules-them-all.html I wonder how we can know about the gravitational lens, how can we even be sure it is there? Would that be only by analyzing the image of the supposed distant galaxi? Which kind of analysis? Or are there other footprints? I am specially impressed by the fact that the distance of the lens is known. How can that be knonw?