A lens is a transmissive optical device that refracts light beams. The lens focuses or disperses light beams. A simple lens is a small piece of a transparent material. A compound lens consists of multiple lenses arranged along with a common axis. A lens focuses a beam of light to form an image. There are two main types of lenses including Convex Lens (Converging) and Concave Lens (Diverging). However, there are many other variations of lenses such as convex concave lenses, biconvex, plano convex, positive meniscus, negative meniscus, plano concave and biconcave. Different applications require different types of lenses.