Bookmark Magnifier

A Fresnel lens replaces the curved surface of a conventional lens with a series of concentric grooves. Originally developed by Augustin-Jean Fresnel in France, these lenses were first made of glass and used to amplify light in lighthouses. New technology and materials allow thin plastic sheets to be molded with concentric circles, creating a lightweight, inexpensive Fresnel lens.
The grooves act as individual refracting surfaces, like tiny prisms, bending parallel rays in a very close approximation to a common focal length. Industrial Fresnel lenses are still used in light-gathering applications and, of course, as magnifying glasses.