A lens is an optical device with perfect or approximate axial
symmetry which transmits and refracts light, converging or
diverging the beam. A simple lens consists of a single optical
element. A compound lens is an array of simple lens with a
common axis; the use of multiple elements allows more optical
abberations to be corrected than is possible with a single element.
Lens are typically made of optical glass(or common glass).Elements
which refract electromagnetic radiation outside the visual spectrum
are also called lenses: for instance, a microwave lens can be made
from paraffin wax.
