A typical Fresnel Lens is made up of many small narrow concentric rings.
Theoretically speaking, each ring can be considered as an individual small lens that
bends the light path.
In fact, the curvature in each ring is approximated by a flat surface
so that each ring behaves like an individual wedge prism:
The advantage of using a Fresnel lens is its compact size compared with a conventional
lens. Common usage includes overhead projectors, pocket-size magnifiers and
motion detectors.
The word "Fresnel" comes from the person who first used this design to construct
lighthouse lenses, Augustin-Jean Fresnel, in 1820. The idea of dividing a lens surface
into concentric rings in order to reduce weight and size, however, can be dated back to
1748 by Georges-Louis Leclerc.
Fresnel Lenses can be made from plastic or glass. There are also different design
variations such as Positive Fresnel Lens, Negative Fresnel Lens, Cylindrical Fresnel
Lens, Fresnel Lens Array, Linear Fresnel
Lens, Lenticular Lens and Fresnel Prism.
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