Achromatic Lens
DETAILS: An achromatic lens is a compound lens system, forming an image free from chromatic aberration.
It works by having two lenses with different refractive properties work together. There is some controversy over exactly who first made an achromatic lens. While John Dollond*, a British telescope maker (1706-1761) patented the discovery, it is widely thought that he actually learned about it from George Bass. A much earlier description is thought to have originated with tne seventeenth century mathematician David Gregory.
Bass in turn, it is believed, came upon the idea sometime in the 1730s when two optical shops sub-contracted jobs to him from the same man, Chester More Hall*: one job was for a lens of flint glass, the other a lens of crown glass.
Hall had found that flint glass appeared to have greater color dispersion than crown glass at the same magnifications. He worked out that cementing the concave face of a flint glass lens to the convex face of a crown glass lens could remove the dispersion properties. Bass realised what Hall was attempting to do, and used the principle in his own telescopes. Twenty years later, Bass met Dollond, and the secret was out.
ONELINER: The achromatic lens
OTHER CONNECTIONS: None
BIBLIOGRAPHY:
http://micro.magnet.fsu.edu/optics/timeline/people/dollond.html
AUDIO/VISUAL: http://www.yorku.ca/eye/achromat.htm – diagram of how the lens focuses white light.