A Coddington magnifier is a
magnifying glass consisting of a single very thick
lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...
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
William Hyde Wollaston (; 6 August 1766 – 22 December 1828) was an English chemist and physicist who is famous for discovering the chemical elements palladium and rhodium. He also developed a way to process platinum ore into malleable ingot ...
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
Sir David Brewster KH PRSE FRS FSA Scot FSSA MICE (11 December 178110 February 1868) was a British scientist, inventor, author, and academic administrator. In science he is principally remembered for his experimental work in physical optics ...
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
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
as the glass. He therefore used a sphere from a single piece of glass with a deep groove cut in it. In 1829,
Henry Coddington
Henry Coddington (1798/9, Oldbridge, County Meath — 3 March 1845, Rome) was an Anglo Irish natural philosopher, fellow and tutor of Trinity College, Cambridge and Church of England clergyman.
Life
Henry Coddington was the son of Latham Coddi ...
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.
''History of Science''
Williams, Book 4, chapter V.
See also
* Stanhope lens
References
{{Reflist
External links
''Build a Coddington''
Magnifiers
Lenses