Thursday, January 17, 2008

Useful information about Lens

A lens is a device for either the concentrating or diverging light, generally formed from a piece of shaped glass. The Analogous devices used with other types of electromagnetic radiation are as well called lenses: for example, a microwave lens can be made from paraffin wax.
The earliest proofs of lenses date to Ancient Greece, with Aristophanes' play The Clouds (424 BC) stating a burning-glass (a convex lens used to focus the sun's rays to create fire). The writings of Pliny the Elder (23-79) as well show that burning-glasses were identified to the Roman Empire, and mentions what is perhaps the first use of a corrective lens: Nero was identified to watch the gladiatorial games through a concave-shaped emerald (most probably to correct for myopia). Seneca the Younger (3 BC--65) explained the magnifying outcome of a glass globe filled with water. The Arabian mathematician Ibn Sahl (c.940-c.1000) used what is at present known as Snell's law to work out the shape of lenses, and Alhazen (Abu Ali al-Hasan Ibn Al-Haitham) (965-1038) wrote the first most important optical treatise which described how the lens in the human eye shaped an image on the retina. Widespread use of lenses did not occur until the invention of spectacles, possibly in Italy in the 1280s.


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