Copy of Snell's Law for Spherical and Parabolic Lenses
Parallel rays of light 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 the lens surfaces can be either spherical or parabolic and the curvature of each surface can be controlled separately. The indices of refraction inside and outside the lens are controlled individually.