Concave & Convex Lens

A concave lens is a type of transparent medium made of glass that has one or two concave surfaces. The best way to recognize a concave lens is by checking the curved surface. It resembles the inner surface of a hollow sphere, almost like the mouth of a cave. These lenses are also called divergent lenses as the parallel beams incident on their surface tends to diverge from their paths.

In a convex lens (sometimes called a positive lens), the glass (or plastic) surfaces bulge outwards at the centre. A convex lens is also called a converging lens because the parallel light rays moving through it curves inward and touches (converges) at a position just beyond the lens known as the focal point.