eyepiece (ocular) An eye lens, a fixed diaphragm with cross-wires, and a field lens, all contained in a short tube which is inserted into the top of a microscope. The internal construction of the eyepiece may vary depending on whether the focal plane lies above (Huygenian or negative eyepiece) or below (Ramsden or positive eyepiece) the field lens. Most eyepieces are either 5× or 10× magnification.

eye·piece / ˈīˌpēs/ • n. the lens or group of lenses that is closest to the eye in a microscope, telescope, or other optical instrument.

eyepiece (ocular) The lens or system of lenses in an optical instrument that is nearest to the eye. It usually produces a magnified image of the previous image formed by the instrument.