Ramsden eyepiece

noun

, Optics.

1. an eyepiece consisting of two plano-convex crown-glass lenses of equal focal length, placed with the convex sides facing each other and with a separation between the lenses of about two-thirds of the focal length of each.

Word History and Origins

Origin of Ramsden eyepiece¹

1840–50; named after Jesse Ramsden (1735–1800), English maker of astronomical instruments