Snell's Law for Spherical and Parabolic Lenses

Parallel rays of light coming from the top of the page encounter a lens. Snell's law is used to track each ray as it is refracted on entering the lens and again on exiting the lens. The shape of each lens surface can be set to planar, spherical, parabolic, or hyperbolic and the curvature of each surface can be controlled separately. The indices of refraction inside and outside the lens are controlled individually.