Magnifying Glass: A medium bounded by two spherical refracting surfaces is referred to a a spherical lens. If the thickness of such a lens is very small compared to object and image distances and to the radii of curvature of the refracting surfaces then the lens is referred to as a thin spherical lens. In general, a lens may have non spherical refracting surfaces. However, most lenses employed in optical systems have spherical refracting surfaces. Therefore, we’ll simply use term ‘lens’ to imply a spherical lens. Different types of lenses are there. The line joining the centers of curvature of the spherical refracting surfaces is referred to as the axis of the lens. Different lenses have different applications. These lenses are used in our contact lens, telescope, microscope even in our eye. Therefore the more details about the applications of these lenses are given in this section.