Kellner
/ˈkɛlnə/noun
1Attributive Designating a compound eyepiece used especially for telescopes, consisting of a planoconvex field lens and an eye lens that is an achromatic doublet.
2A Kellner eyepiece.
Origin
Mid 19th century; earliest use found in Proceedings of the Royal Society of London. From the name of Karl Kellner, German optical instrument maker, who introduced the eyepiece in 1849.