Ray pencils of general divergency

African Vision and Eye Health

Field Value
Title Ray pencils of general divergency
Creator Harris, W. F.
Subject — asymmetric dioptric power; vergence; step-along procedures; focal lines; divergency; divergence
Description That a thin refracting element can have a dioptric power which is asymmetric immediately raises questions at the fundamentals of linear optics.  In optometry the important concept of vergence, in particular, depends on the concept of a pencil of rays which in turn depends on the existence of a focus.  But systems that contain refracting elements of asymmetric power may have no focus at all.  Thus the existence of thin systems with asym-metric power forces one to go back to basics and redevelop a linear optics from scratch that is sufficiently general to be able to accommodate suchsystems.  This paper offers an axiomatic approach to such a generalized linear optics.  The paper makes use of two axioms: (i) a ray in a homogeneous medium is a segment of a straight line, and (ii) at an interface between two homogeneous media a ray refracts according to Snell’s equation.  The familiar paraxial assumption of linear optics is also made.  From the axioms a pencil of rays at a transverse plane T in a homogeneous medium is defined formally (Definition 1) as an equivalence relation with no necessary association with a focus.  At T the reduced inclination of a ray in a pencil is an af-fine function of its transverse position.  If the pencilis centred the function is linear.  The multiplying factor M, called the divergency of the pencil at T, is a real  2 2×  matrix.  Equations are derived for the change of divergency across thin systems and homogeneous gaps.  Although divergency is un-defined at refracting surfaces and focal planes the pencil of rays is defined at every transverse plane ina system (Definition 2).  The eigenstructure gives aprincipal meridional representation of divergency;and divergency can be decomposed into four natural components.  Depending on its divergency a pencil in a homogeneous gap may have exactly one point focus, one line focus, two line foci or no foci.Equations are presented for the position of a focusand of its orientation in the case of a line focus.  All possible cases are examined.  The equations allow matrix step-along procedures for optical systems in general including those with elements that haveasymmetric power.  The negative of the divergencyis the (generalized) vergence of the pencil.
Publisher AOSIS
Date 2009-12-13
Type info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion — —
Format application/pdf
Identifier 10.4102/aveh.v68i2.160
Source African Vision and Eye Health; South African Optometrist: Vol 68, No 2 (2009); 97-110 2410-1516 2413-3183
Language eng
Relation https://avehjournal.org/index.php/aveh/article/view/160/129
Coverage — — —
Rights Copyright (c) 2009 W. F. Harris https://creativecommons.org/licenses/by/4.0