Assertion: visby lens | /r/AtLocation | viking treasures
Facets:
value: on the island of gotland
type: LOCATION
Source sentences:
text: The Visby lenses found in Viking treasures on the island of Gotland dating from the 10th or 11th century are also aspheric, but exhibit a wide variety of image qualities, ranging from similar to modern aspherics in one case to worse than spheric lenses in others.