parfocal eyepieces

parfocal eyepieces

[pär′fō·kəl ′ī‚pēs·əz]
(optics)
Eyepieces whose lower focal points lie in the same plane, so that they can be interchanged without changing the focus of the instrument with which they are used.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Parfocal eyepieces are needed to keep the arm positioned in its nominally ideal spot.
The focus travel is almost 1 1/2 inches, which, while adequate for so-called parfocal eyepieces, could be a problem for anyone with a set of eye-pieces that span a wide range of focal positions.