Fresnel lens

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A Fresnel lens (pronounced /freɪˈnɛl/ fray-NELL) is a type of lens originally developed by French physicist Augustin-Jean Fresnel for lighthouses.

The design enables the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design. Compared to conventional bulky lenses, the Fresnel lens is much thinner, larger, and flatter, and captures more oblique light from a light source, thus allowing lighthouses to be visible over much greater distances.

Contents

History

The idea of creating a thinner, lighter lens by making it with separate sections mounted in a frame is often attributed to Georges-Louis Leclerc, Comte de Buffon.[1] The marquis de Condorcet (1743–1794) proposed grinding such a lens from a single thin piece of glass.[2] French physicist and engineer Augustin-Jean Fresnel is most often given credit for the development of the multi-part lens for use in lighthouses. According to Smithsonian magazine, the first Fresnel lens was used in 1823 in the Cordouan lighthouse at the mouth of the Gironde estuary; its light could be seen from more than 20 miles (32 km) out.[3] Scottish physicist Sir David Brewster is credited with convincing the United Kingdom to adopt these lenses in their lighthouses.[4][5]

Description

The Fresnel lens reduces the amount of material required compared to a conventional spherical lens by dividing the lens into a set of concentric annular sections known as "Fresnel zones", which are theoretically limitless.[6]

In the first (and largest) variations of the lens, each zone was actually a separate prism. Though a Fresnel lens might appear like a single piece of glass, closer examination reveals that it is many small pieces. It was not until modern computer-controlled milling equipment (CNC) could turn out large complex pieces that these lenses were manufactured from single pieces of glass.

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