Search Menu
Photonics Media Photonics Marketplace Photonics Spectra BioPhotonics Vision Spectra Photonics Showcase Photonics ProdSpec Photonics Handbook
Lambda Research Optics, Inc. - Limited Time Offer
Photonics Dictionary


An ophthalmic instrument used to measure the magnitude and direction of the maximum and minimum powers of a spectacle lens, and mark the optical center of the lens by an ink dot. When the lens to be measured is placed in a beam of parallel light between a collimator and projection lens, the X-shaped reticle at the focus of the collimator rotates and moves along the axis until a sharp focus is seen on a ground-glass screen or in an eyepiece. Abbe pointed out that if the rear vertex of the test lens is at the anterior focus of the collimator lens, then the longitudinal movement of the reticle will be strictly proportional to the vertex power of the spectacle, and that the size of the reticle image will be independent of the power of the test lens.
back to top
Facebook Twitter Instagram LinkedIn YouTube RSS
©2023 Photonics Media, 100 West St., Pittsfield, MA, 01201 USA, [email protected]

Photonics Media, Laurin Publishing
x We deliver – right to your inbox. Subscribe FREE to our newsletters.
We use cookies to improve user experience and analyze our website traffic as stated in our Privacy Policy. By using this website, you agree to the use of cookies unless you have disabled them.