Seeing 20/20 in 2020
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses, usually arranged along a common axis.
Lenses are made from glass or plastic and are ground and polished or molded to a desired shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing.
The word lens comes from lēns, the Latin name of the lentil, because a bi-convex lens is lentil-shaped.