negative principal planes
negative principal planes[′neg·əd·iv ¦prin·sə·pəl ′plānz]
Two planes perpendicular to the optical axis such that objects in one plane form images in the other with a lateral magnification of -1. Also known as antiprincipal planes.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.