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Chapter-04 Transposition

BOOK TITLE: Optician’s Guide (A Mannual for Opticians)

Author
1. Bhootra Ajay Kumar
ISBN
9789351528241
DOI
10.5005/jp/books/14237_5
Edition
3/e
Publishing Year
2018
Pages
8
Author Affiliations
1. Kolkata, India, Kolkata, West Bengal, India, Diploma in Sportvision (UK), Krishnalaya School of Optometry, Kolkata, West Bengal, India, ICLEP FIACLE (Australia); (UK)
Chapter keywords
Transposition, lens, lens power, meridian value, transposition rule, double cylinder form, spherocylinder form

Abstract

This chapter aims to present a detailed discussion on transposition of lenses. Transposition of lenses is to rewrite the expressions of its power without actually changing them. It implies transfer of lens power from one form to another so as to their meridian values remain the same in both the forms. When we get a lens power first we draw the two principal meridians according to the direction of axis. Now put the spherical power on the axis meridian and the sum of spherical and cylindrical power on the opposite meridian. To transfer the meridian values to lens power, we take lower meridian value as spherical and the difference of the two meridian values as cylindrical. There are three ways in which a lens power may be written which are mentioned in this chapter. This chapter also covers different transposition rules with the help of suitable examples.

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