Talk:Visby lenses

From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Norse history and culture (Rated B-class, Low-importance)
WikiProject icon This article is within the scope of WikiProject Norse history and culture, a WikiProject related to all activities of the North Germanic peoples, both in Scandinavia and abroad, prior to the formation of the Kalmar Union in 1397. If you would like to participate, you can edit the article attached to this page, or visit the project page, where you can join the project and/or contribute to the discussion.
B-Class article B  This article has been rated as B-Class on the project's quality scale.
 Low  This article has been rated as Low-importance on the project's importance scale.
WikiProject Glass  
WikiProject icon This article is within the scope of WikiProject Glass, a collaborative effort to improve the coverage of glass on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
 ???  This article has not yet received a rating on the quality scale.
 ???  This article has not yet received a rating on the importance scale.

What needs to be added[edit]

The lenses were dated to the 10th century, but when where they found, and who found them? Where can they be seen now? How do we 'know' what they were for? ~Bengaley

On a funny note--did anyone else get the mental image of the stereotypical hairy scary Viking with a monocle? It popped into MY head, anyway... (talk) —Preceding undated comment was added at 22:01, 2 September 2008 (UTC)

A small dose of cold water ...[edit]

A lens with a focal length of 22 mm and F-number of 0.5 is practically useless for building a telescope, spherical aberration or not. It would do better as a burning glass, although for that purpose spherical aberration is irrelevant, diameter is everything (and 50 mm diameter is ok-ish, not great.)

The thing that these lenses would be good for, if indeed they are lenses, is as a "chart glass". That is, you lay it on a page of text and read a magnified view of the text. Good for reading fine print on nautical charts, and probably ok for reading books when your eyes are failing (but rather awkward compared to spectacles.)

On the other hand, so far as I am aware 12th century Vikings didn't have books ... -- (talk) 17:33, 16 September 2009 (UTC)

Please correct the units[edit]

The second paragraph under "Description" mentions "an angular resolution of 25–30 μm", which is as self-evidently ridiculous as anything ever gets. Angular resolution is measured in angular units and not linear ones (duh). Maybe what's quoted is the spatial equivalent of angular resolution, but if so, then please also indicate where it is measured with respect to the lens. — Preceding unsigned comment added by (talk) 17:38, 4 October 2011 (UTC)

Moreover, there is no reference for this measurement. In the cited papers, I found only the numbers for the variation of focal length with aperture (1mm for the best specimen — one which has not been preserved, and is discussed only based on a photo). Additionally, in the references they discuss only the optical performance of lenses with similar and exactly elliptical shapes, not the shapes of the actually present specimens. The residual variation w.r.t. best-fitting ellipse is about 0.4mm–1.5mm. For comparison, recall that usually required precision of optically sound refractive surfaces is below wavelength/2, so below 0.0003mm. — iz

Contradiction with another page[edit]

These two pages contradict each other on the optical quality of the Visby lenses: The Visby lenses...exhibit a wide variety of image qualities.... (The lenses) are so well produced that even computer optimisation has not been able to improve their performance. — Preceding unsigned comment added by Lriley47 (talkcontribs) 03:20, 24 April 2015 (UTC)