Visby Lens

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Photo: Visby lens displayed at the Museum of National Antiquities in Stockholm. By mararie. Used under the Creative Commons Attribution-Share Alike 2.0 Generic Licence.

Polished rock crystals set in silver have not been found anywhere in the Nordic regions except on Gotland. They turn up among hoards and grave goods from the transition period between the Viking Age and the Medieval Period and they also appear during this period out in Europe.

Large natural deposits of rock crystal have been discovered in the Alps, although the silver-mounted rock crystals on Gotland probably emanate from Persia, when the town of Basra was a renowned centre for crystal crafts during the prehistoric periods.

Most of the rock crystals on Gotland are lens-shaped and the ornamentation on the mount suggests that they were already set in the silver mounts when imported from the Slavic regions. The ornamentation on the mount of the spherical crystals differs and might well have been created on Gotland.

The polished rock crystals have a magnifying effect, which has led to theories of them having been used as magnifying glasses. Suggestions have even been put forth that they were used as navigational aids. The most commonly accepted interpretation, however, is that they were worn as adornment.

http://www.gotmus.i.se/1engelska/skatter/engelska/jewellery_as_form_of_personal_expression.htm

Viking Lenses from Visby, Sweden

Several 11th century hoards found at Viking sites on the island of Gotland, Sweden, contained biconvex lenses made from rock-crystal. Some of them were set in silver. A few lenses had an almost perfect elliptical shape. The symmetry of the lenses as well as their biconvex elliptical form and fine polish, which resulted in a very good imaging, made a sensation when discovered by modern scientists. The idea of producing at such an early date quality lenses that could be almost as accurate as those of modern optics, was something unheard of.

The results of research concerning the lenses from the Viking sites were published in November 1998 by Dr Karl-Heinz Wilms, Dr Olaf Schmidt, and Prof. Dr Bernd Lingelbach from Aalen University of Applied Science (Fachhochschule Aalen). The late Dr Wilms first heard of rock-crystal lenses from Gotland, an island in the Baltic Sea, in 1990, when he was selecting exhibits for a museum in Munich. The lenses became widely known as Visby lenses, after the major town on Gotland. The team of three scientists arrived there in 1997 to make a surprising discovery concerning the Viking Age technology. After a series of tests it became clear that the quality of the 11th century rock-crystal lenses made on a turning lathe nearly equaled that of modern samples made with CNC machines (CNC stands for Computer Numerical Control).
The use of the Visby lenses is a matter of some controversy. Some of them look like jewelry, but it is unlikely that they were merely ornaments. They could serve as magnifiers, which allowed to carry out fine carving, to start fires or to burn cuts and wounds in order to prevent infection. Taking into account the outstanding quality of the lenses, it was even possible that the Vikings might use them to construct a telescope.

It is unclear where the lenses were manufactured. M. Stenberger believes that the rock-crystal was brought from the Middle East to western or south-western Russia, where it could be set in silver. There it might be bought by merchants from Gotland. According to another version, the lenses were brought to Sweden from Byzantium by a member of the Varangian Guard, personal Viking bodyguards of the Byzantine emperors.
Part of the lenses are exhibited in the Historical Museum in Visby as well as in the Swedish National Museum in Stockholm and other collections. Some of the lenses were lost.

http://www.vikingrune.com/2009/01/viking-lenses-visby/

Titre du document / Document title

The visby lenses

Auteur(s) / Author(s)

SCHMIDT O. ⁽¹⁾ ; WILMS K.-H. ⁽²⁾ ; LINGELBACH B. ⁽¹⁾

;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

⁽¹⁾ Aalen University of Applied Science, Aalen, ALLEMAGNE
⁽²⁾ Ophthalmic Instruments Rodenstock, Emmering, ALLEMAGNE

Résumé / Abstract

Purpose. In this study, 10 lens-shaped rock crystals, manufactured not later than the early Middle Ages, have been examined with respect to their image-forming qualities. Methods. The spherical aberration of the lenses served as a scale for comparison. Measurements have been taken with a specially designed light section method. Some of the examined lenses have a silver mounting and have been used as pendants, whereas others are unmounted and show no signs of use as jewelry. Results. The two largest unmounted lenses have very interesting surface curvatures, rendering a very small spherical aberration of the lens. The combination of top and bottom surfaces of the lens causes an imaging quality comparable to the modern aspheric lenses used, e.g., in today’s projectors. Conclusion. According to the results of this study, the knowledge and comprehension of optical design was much further developed in the Middle Ages than we assume today.

Revue / Journal Title

Optometry and vision science   ISSN 1040-5488   CODEN OVSCET

Source / Source

1999, vol. 76, n^o9, pp. 624-630 (8 ref.)

Langue / Language

Anglais

Editeur / Publisher

Lippincott Williams & Wilkins, Hagerstown, MD, ETATS-UNIS  (1989) (Revue)

Mots-clés anglais / English Keywords

Aspherical lens ; Design ; Crystals ; Rocks ; Human ; History ; Instrumentation therapy ;

Mots-clés français / French Keywords

Lentille asphérique ; Conception ; Cristal ; Roche ; Homme ; Histoire ; Traitement instrumental ;

Mots-clés espagnols / Spanish Keywords

Lente asférico ; Diseño ; Cristal ; Roca ; Hombre ; Historia ; Tratamiento instrumental ;

Localisation / Location

INIST-CNRS, Cote INIST : 6826, 35400008989734.0040

http://cat.inist.fr/?aModele=afficheN&cpsidt=1985794

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