Lenses are used in cameras, telescopes, binoculars, microscopes and corrective glasses. A lens can be converging (convex) or diverging (concave).

A plano-concave lens is a lens with one side being flat and the other side being concave. It is characterized by being thin in the center and thick at the edges, and can make parallel light rays ...

Shanghai Optics Inc - Plano Concave LensesA 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, ...

The lens is produced by blocky, S-shaped “unit cells” a few millimeters wide that refract radio waves in particular directions. The roughly concave lens is formed from 4,000 of these cells.

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 ...