A point-mass lens and an extended source

In this case the deflection angle, the deflection potential, the lens equation and the critical curves and caustics are the same as in the previous one, because they are the lens’ characteristic. The difference is that now the images are not point-like, they are extended, forming a ring when β=0 and two arcs otherwise. When the source is very far from the lens in the plane of the sky we will see a single image.