Excavations at the Viking harbour town of Fröjel, Gotland, Sweden

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Excavations at the Viking harbour town of Fröjel, Gotland, Sweden

Post by jancancook on Mon Mar 28, 2011 8:02 am

Excavations at the Viking harbour town of Fröjel, Gotland, Sweden discovered in 1999 the rock crystal Visby lenses, produced by turning on pole-lathes at Fröjel in the 11th to 12th century, with an imaging quality comparable to that of 1950s aspheric lenses. The Viking lenses were capable of concentrating enough sunlight to ignite fires.[9]

Widespread use of lenses did not occur until the use of reading stones in the 11th century and the invention of spectacles, probably in Italy in the 1280s. Scholars have noted that spectacles were invented not long after the translation of Ibn al-Haytham's Book of Optics into Latin, but it is not clear what role, if any, the optical theory of the time played in the discovery.[5][10] Nicholas of Cusa is believed to have been the first to discover the benefits of concave lenses for the treatment of myopia in 1451.

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