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Recent excavations at the Viking harbor town of Fröjel, Gotland in Sweden have revealed a small number of rock crystal lenses known as the Visby lenses.
These may have been made using pole-lathes.
They have an imaging quality comparable to that of 1950s aspheric lenses.
The Viking lenses effectively concentrate sunlight enough to ignite fires ; however it is not known whether they were used for this purpose.
Similar technology may have been used in ancient Ireland ( the Liath Meisicith ) and quite possibly ancient Egypt.
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