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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.
Lockheed XF-90. The Lockheed XF-90 was built in response to a United States Air Force requirement for a long-range penetration fighter and bomber escort. The same requirement produced the McDonnell XF-88 Voodoo. Lockheed received a contract for two prototype XP-90 s (redesignated XF-90 in 1948). The design was developed by Willis Hawkins and ...
Welding helmet. A welding helmet in use. A welding helmet is a type of personal protective equipment used in performing certain types of welding to protect the eyes, face, and neck from flash burn, sparks, infrared and ultraviolet light, and intense heat. The modern welding helmet used today was first introduced in 1937 by Willson Products.
These new lenses included 35–80 mm f /4–5.6 (with built-in lens cap), 80–200 mm f /4.5–5.6, 35–105 mm f /3.5–4.5, 70–210 mm f /3.5–4.5, and 100–300 mm f /4.5–5.6. [ 4 ] Some of the original lenses were updated and re-released with the same cosmetics and are known as "New" or "Restyled" versions; minor optical updates such as ...
A gradient-index lens with a parabolic variation of refractive index (n) with radial distance (x). The lens focuses light in the same way as a conventional lens. Gradient-index (GRIN) optics is the branch of optics covering optical effects produced by a gradient of the refractive index of a material. Such gradual variation can be used to ...
Lens speed. A fast prime (fixed focal length) lens, the Canon 50mm f/ 1.4 (left), and a slower zoom lens, the Canon 18–55mm f/ 3.5–5.6 (right); this lens is faster at 18mm than it is at 55mm. Lens speed is the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens with a larger than average maximum aperture (that is ...
35 mm equivalent focal length. The resulting images from 50 mm and 70 mm lenses for different sensor sizes; 36x24 mm (red) and 24x18 mm (blue) In photography, the 35 mm equivalent focal length is a measure of the angle of view for a particular combination of a camera lens and film or image sensor size. The term is popular because in the early ...
Petzval portrait lens. The Petzval objective, or Petzval lens, is the first photographic portrait objective lens (with a 160 mm focal length) in the history of photography. [ 1 ] It was developed by the Slovak mathematics professor Joseph Petzval in 1840 in Vienna, [ 2 ] with technical advice provided by Peter Wilhelm Friedrich von Voigtländer ...
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