Original Research

Graphical construction of cardinal points from the transference

W. F. Harris
African Vision and Eye Health | South African Optometrist: Vol 70, No 1 | a88 | DOI: https://doi.org/10.4102/aveh.v70i1.88 | © 2011 W. F. Harris | This work is licensed under CC Attribution 4.0
Submitted: 09 December 2011 | Published: 10 December 2011

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W. F. Harris, Department of Optometry, University of Johannesburg

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Abstract

Usually nodal, principal and focal points are defined independently and thought of as distinct structures with no simple relationship among them.  By adopting a holistic approach, in which these threetypes of cardinal points are treated as particular cases of a larger class of special points, this paper develops a method of constructing the locations of the cardinal points of a system graphically directly from the transference.  The method provides a useful way of visualising the relationship of the locations of the cardinal points and of how they are affected by changes in the system or when a second optical system is placed in front of the first.  Thepaper illustrates the graphical procedure by apply-ing it in several situations of interest in optometryand ophthalmology, including the effect of a contact lens or refractive surgery on a reduced eye and the effect of accommodation, a spectacle lens and an afocal telescope on the Gullstrand-Emsley
schematic eye. (S Afr Optom 2011 70(1) 3-13)


Keywords

Cardinal point, nodal point; principal point; focal point; transference

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