Coddington magnifier
Image:Coddington-magnifier.svg
A Coddington magnifier is a magnifying glass consisting of a single very thick lens with a central deep groove diaphragm at the equator, thus limiting the rays to those close to the axis, which minimizes spherical aberration. This allows for greater magnification than a conventional magnifying glass, typically 10× up to 20×. Most single lens magnifiers are limited to 5× or so before significant distortion occurs. The drawback is that the diaphragm groove reduces the area seen through the magnifier.
History
In 1812 William Hyde Wollaston introduced a much improved version of the earliest magnifiers consisting of a spherical glass by employing two hemispheres of glass mounted together with a small stop between them. Sir David Brewster found that Wollaston's form worked best when the two lenses were hemispheres and the central space was filled up with a transparent cement having the same refractive index as the glass. He therefore used a sphere from a single piece of glass with a deep groove cut in it.[https://archive.org/stream/introductionappl032651mbp/introductionappl032651mbp_djvu.txt An Introduction To Applied Optics, Volume II], L. C. Martin, Sir Isaac Pitman & Sons, Ltd, London, 1932. In 1829, Henry Coddington brought the Wollaston–Brewster lens into general notice and further refined the design by modifying the shape of the groove, though Coddington laid no claim to being its inventor.[http://www.cosmovisions.com/Williams040503.htm History of Science], Williams, Book 4, chapter V.
See also
References
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External links
- [http://www.gadgetbuilder.com/Coddington.html Build a Coddington]