Source: NOVA: "Galileo's Battle for the Heavens" This resource was adapted from NOVA: "Galileo's Battle for the Heavens." As early as the 1300s, eyeglasses made from convex, or outward-curving, lenses ...

A plano concave lens is an optical lens with one concave surface and one flat surface. It has a negative focal length, and can be used for light projection, beam expansion, or to increase focal length ...