Imaging with a gravitational lens: the geometric view

We investigate imaging point sources with a monopole gravitational lens, such as the Solar Gravitational Lens in the geometric optics limit. We compute the light amplification of the lens used in conjunction with a telescope featuring a circular aperture that is placed in the focal region of the lens, compared to the amount of light collected by the same telescope unaided by a gravitational lens. We recover an averaged point-spread function that is in robust agreement with a wave-theoretical description of the lens, and can be used in practical calculations or simulations.