Patent US 4,474,437

A lens for simulating the effect of gravity from a galaxy on light from a source effectively positioned at infinity with the light passing through the galaxy, the optical properties of the lens being equivalent to that of a lens having a flat plane surface on one side and a compound curved surface on the other side. The lens is rotationally symmetric about a central axis. The compound curve surface includes a convex region in the center thereof and a cusp shaped region in the outer edges thereof, said cusp shaped region being shaped nearly flat and parallel to the flat plane surface on the other side of the lens at the outer edge thereof. The convex region merges into the cusp shaped region through a flat plane prismatic region. The focal length of the convex region is less than the distance between the lens and the observer ensuring that the observer holding the lens (approximately at arm's length) on viewing an object through said lens will see multiple images of said object. This will simulate what an observer would see if the light from such an object were passing through a transparent galaxy located between the observer and the object.