It is a lens that possesses at least one surface that curves inwards. When light rays are incident on a concave lens, they bend outwards or diverge. The rays diverge away from each other. Thus, a concave lens is also called a diverging lens. A concave lens is thinner at its centre than at its edges, and is used to correct short sightedness. It does not focus at a single point. The image formed by a concave lens is upright, virtual and smaller than the object. For example, the images seen through a peephole are different from normal holes, because these peep holes contain concave lenses.