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A Fresnel lens ( / ˈfreɪnɛl, - nəl / FRAY-nel, -nəl; / ˈfrɛnɛl, - əl / FREN-el, -əl; or / freɪˈnɛl / fray-NEL [1]) is a type of composite compact lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections.
The Peli Lens is a mobility aid for people with homonymous hemianopia. It is also known as “EP” or Expansion Prism concept and was developed by Dr. Eli Peli of Schepens Eye Research Institute in 1999. It expands the visual field by 20 degrees.
Polarized sunglasses block the s polarization, greatly reducing glare from horizontal surfaces. The Fresnel equations (or Fresnel coefficients) describe the reflection and transmission of light (or electromagnetic radiation in general) when incident on an interface between different optical media.
This phase difference is not explicitly dependent on wavelength, but only on refractive index, so Fresnel rhombs made of low-dispersion glasses achieve much broader spectral range than quarter-wave plates. They displace the beam, however. Doubled Fresnel rhomb, with quadruple reflection and zero beam displacement, substitutes a half-wave plate.
This is most commonly achieved through the use of Fresnel prisms. These slim flexible plastic prisms can be attached to the patient's glasses, or to plano glasses if the patient has no refractive error, and serve to compensate for the inward misalignment of the affected eye.
Durable Fresnel lenses can be molded from plastic and are inexpensive. Lenticular lenses are arrays of microlenses that are used in lenticular printing to make images that have an illusion of depth or that change when viewed from different angles.
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