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Lens sag is a problem that sometimes afflicts very large refracting telescopes. It is the equivalent of mirror sag in reflecting telescopes. It occurs when the physical weight of the glass causes a distortion in the shape of the lens because the lens can only be supported by the edges. A mirror on the other hand can be effectively supported by the entire opposite face, making mirror sag much less of a problem. One expensive solution to lens sag is to place the telescope in orbit around the Earth.
The technical limit concerning lens sag was reached at the Yerkes refractor (1897) with an aperture of 40" (102 cm), where the sagging already causes small optical distortions. The 1890s therefore mark the end of the great refractors era.
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Lens
Lens may refer to:
Optics
- Lens (anatomy), a part of the eye
- Corrective lens for correction of human vision
- Contact lens, placed on the cornea of the eye
- Camera lens, a lens designed for use on a camera
- Contact lens, placed on the cornea of the eye
Other radiation focus and forces
Places
Lens (optics)
A lens is a transmissive optical device that affects the focus of a light beam through refraction. A simple lens consists of a single piece of material, while a compound lens consists of several simple lenses (elements), usually along a common axis. Lenses are made from transparent materials such as glass, ground and polished to a desired shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly refract radiation other than visible light are also called lenses, such as microwave lenses or acoustic lenses.
History
The word lens comes from the Latin name of the lentil, because a double-convex lens is lentil-shaped. The genus of the lentil plant is Lens, and the most commonly eaten species is Lens culinaris. The lentil plant also gives its name to a geometric figure.
The variant spelling lense is sometimes seen. While it is listed as an alternative spelling in some dictionaries, most mainstream dictionaries do not list it as acceptable.
Lens (surname)
Lens is a surname. Notable people with the surname include:
SAG
SAG is the acronym for:
- Screen Actors Guild Awards (also known as the SAG Award)
SAg is the abbreviation for:
Sag (or Sâg, Șag, Šag) may refer to:
Sag (geology)
In geology a sag, or trough, is a depressed, persistent, low area; the opposite of an arch, or ridge, a raised, persistent, high area. The terms sag and arch were used historically to describe very large features, for example, characterizing North America as two arches with a sag between them.
Also, a sag is a former river bed which has been partially filled with debris from glaciation or other natural processes but which is still visible in the surface terrain. Sags formed by the former river beds of large rivers often become the valleys of smaller streams after a change of course by the main river.
Examples of sags include the former continuations of the Grand, Moreau and White rivers in South Dakota in the United States. Before the last ice age these rivers continued eastward past their current confluences with the present course of Missouri River. The sags are prominently visible on the plateau of the Coteau du Missouri, allowing small streams to drain into the Missouri from its eastern side.
2010 South Asian Games
The 2010 South Asian Games, officially the XI South Asian Games, was a major multi-sport event that took place from 29 January to 8 February 2010 in Dhaka, Bangladesh. This was the third time that the Bangladeshi capital hosted the Games, thus becoming the first city to hold the games three times.
Roughly 2000 athletes from eight countries competed at the games in 23 different sports. The sporting giant of the region, India continued its dominance in the game's medal tally with a staggering 175 medals including 90 gold medals. Pakistan narrowly beat the host country in gold medals count with 19, while the host Bangladesh captured 18 golds including the region's most popular and prestigious football and cricket titles. Bangladesh, however, earned second spot in total medal count beating out Pakistan. Sri Lanka’s Shehan Abeypitiya becomes the fastest man while Pakistan’s Naseem Hamid was crowned the fastest woman of the region winning 100 meter sprint.
Organization
The 11th South Asian Games were originally scheduled to take place in November 2009. However, the host country (Bangladesh) faced difficulties due to general elections. As a result, the South Asian Association Council (SAOC) held the 39th Executive Meeting and decided against hosting the Games in 2009, postponing the games to early 2010.
