Eye'-piece, n.

(ī′pēs), n. (Opt.) The lens, or combination of lenses, at the eye-end of a telescope, or other optical instrument, by which the image, formed by the mirror or object-glass, is viewed.

Negative or Huyghenian eye-piece, an eye-piece consisting of two plano-convex lenses with their curved surfaces turned toward the object-glass, and separated from each other by about half the sum of their focal distances, the image viewed by the eye being formed between the two lenses.—Positive eye-piece, an eye-piece consisting of two plano-convex lenses placed with their curved surfaces toward each other, and separated by a distance somewhat less than the focal distance of the one nearest the eye, the image of the object viewed being beyond both lenses;—called also, from the name of the inventor, Ramsden's eye-piece.—Terrestrial or erecting eye-piece, an eye-piece used in telescopes for viewing terrestrial objects, consisting of three, or usually four, lenses, so arranged as to present the image of the object viewed in an erect position.