Porro-prism erecting system

Porro-prism erecting system

[′pȯ·rō ‚priz·əm i′rek·tiŋ ‚sis·təm]
(optics)
A compound erecting system, designed by M. Porro, in which there are four reflections to completely erect the image; two Porro prisms are employed; the line of sight is bent through 360°, is displaced, but is not deviated; used in prism binoculars and some telescope systems.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.