Reading stone (optics)
A reading stone (also known as bright field magnifier , visolet magnifier or glass ) is a very thick, plane-convex lens . It is used as a magnifying glass by placing the flat side directly on a book page or the like.
The visolet magnifier has a 1.8-fold magnification and is characterized by its excellent lighting conditions for the object. The light from the surroundings is collected in the object due to the collecting effect of the magnifying glass. Diffuse lighting is best - that is, a general brightness of the surroundings is better than a point-like light source aimed at the magnifying glass. The brightness of the object is thus greater than that of the surroundings. In order to achieve optimal lens aberration correction, the height of the magnifying glass should be 4/3 of the radius of the spherical segment.
Reading stones were already used in the Middle Ages . From the reading stone, which was originally made of beryl , the monocle and glasses , the name of which goes back to the beryl, were created.
Today reading stones are made of glass or plastic and are mainly used by the visually impaired.
history
Abu Ali al-Hasan ibn al-Haitham , an Islamic scientist and naturalist, is considered to be the mastermind behind the reading stone . However, this is said to have been inspired by Abbas Ibn Firnas . After the translation of his work Kitab-al-Manazir by the monk Witelo , some other members of the order took up the idea and constructed a super-hemispherical planoconvex lens made of quartz or rock crystal. This transparent crystalline stone, through which one sees the letters enlarged when placed on a book page, was described by the Oxford-born Franciscan Roger Bacon in his treatise Opus maius in 1267 ; he also tried to explain the phenomenon and suggested improvements.
Web links
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- ↑ Information from the German Association for the Blind and Visually Impaired (DBSV) here online ( memento of the original from July 6, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Archived copy ( memento of the original from June 21, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
