Reading stone

A reading stone (also bright field magnifier, Visolettlupe or glass ) is a very thick, plano-convex lens. It is used as a magnifying glass, by being placed with the flat side directly on a book page or something similar.

The Visolettlupe has a 1.8x magnification ratio and is distinguished by its excellent lighting conditions for the object. The ambient light is collected due to the accumulating effect of magnifying the object. The best location is a diffuse lighting - that is, a general brightness of the environment is better than that necessary to Lupe, point source of light. The brightness of the object is thus larger than that of the environment. To achieve an optimum error correction lens, the height of the microscope 4/3 should be the radius of the ball segment.

Reading stones have been used in the Middle Ages. From the reading stone, which was originally made ​​of beryl, monocle and spectacles, whose name is derived from Beryl was born.

Today, reading stones are made of glass or plastic and used primarily by the visually impaired.

History

As a pioneer of the reading stone applies Abu Ali al -Hasan ibn al - Haitham, an Islamic scientists and naturalists. This should be, however, been inspired by Abbas Ibn Firnas. After the translation of his work Kitab -al- Manazir by the monk Vitelo some other Order members took up the idea and constructed a überhalbkugelige plano-convex lens made ​​of quartz or rock crystal. This transparent crystal stone, through which one sees the letters increased when placed on a book page, described originally from Oxford Franciscan Roger Bacon in 1267 in his treatise "Opus majus "; He also tried to explain the phenomenon, and proposed improvements.