What is a Len?. A lens is conventionally defined as a piece of glass which is used to focus or change the direction of a beam of light passing through it.
They are mainly made of glass or plastic. Lens are used in making spectacles, cameras, cinema projectors, microscopes and telescopes.
Types of thin lenses.
A lens which is thicker at its centre than at its edges converges light and is called convex or converging lens.
A lens which is thicker at its edges than at its centre diverges light and is known as concave or diverging lens.