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Internal focusing, which focuses binoculars by moving internal mounted optical lenses located between the objective lens group and the prism assembly – or rarely located between the prism assembly and eyepiece lens assembly [23] [38] – within the housing without changing the volume of the binoculars. The addition of a focusing lens reduces ...
A Fresnel lens (/ ˈ f r eɪ n ɛ l,-n əl / FRAY-nel, -nəl; / ˈ f r ɛ n ɛ l,-əl / FREN-el, -əl; or / f r eɪ ˈ n ɛ l / 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.
Many "N" lenses are the same as their prior "C" or "S" lens version, but have changes to the lens coatings and a plastic aperture ring instead of metal. Some "C" lenses received a cosmetic update (removal of the chrome on the focus ring) but were not otherwise changed and did not receive a "N" marking, such as the 50mm f/4.5 and 500mm f/5.6.
The lenses typically used on DSLRs have a wider range of apertures available to them, ranging from as large as f / 0.9 to about f / 32. Lenses for smaller sensor cameras rarely have true available aperture sizes much larger than f / 2.8 or much smaller than f / 5.6.
Artist's impression of Leonardo's method for neutralizing the refractive power of the cornea. Leonardo da Vinci is frequently credited with introducing the idea of contact lenses in his 1508 Codex of the eye, Manual D, [9] wherein he described a method of directly altering corneal power by either submerging the head in a bowl of water or wearing a water-filled glass hemisphere over the eye.
Refractive surgery causes only minimal size differences, similar to contact lenses. In a study performed on 53 children who had amblyopia due to anisometropia, surgical correction of the anisometropia followed by strabismus surgery if required led to improved visual acuity and even to stereopsis in many of the children [ 9 ] ( see: Refractive ...
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