principal plane

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prin·ci·pal plane

the theoretic plane of a compound lens system. See: principal point.


In geometrical optics, a straight line representing the direction of propagation of light.
axial ray A ray that is coincident with the axis of an optical system.
chief ray A ray joining an object point to the centre of the entrance pupil of an optical system (Fig. R2). See pencil of light.
emergent ray A ray of light in image space either after reflection (reflected ray) or after refraction (refracted ray).
extraordinary ray See birefringence.
incident ray A ray of light in object space that strikes a reflecting or refracting surface.
marginal ray A ray joining the axial point of an object to the edge or margin of an aperture or pupil (Fig. R2).
ordinary ray See birefringence.
paraxial ray A light ray that forms an angle of incidence so small that its value in radians is almost equal to its sine or its tangent. (i.e. sin θ = θ or tan θ = θ. These are approximate expressions referred to as the paraxial approximation (or the gaussian approximation). See paraxial optics; paraxial region; gaussian theory.
principal ray A ray joining the extreme off-axis object point to the centre of the entrance pupil or aperture (Fig. R2).
ray tracing Technique used in optical computation consisting of tracing the paths of light rays through an optical system by graphical methods or by using formulae. Nowadays, computer methods are used. See sign convention.
Fig. R2 Rays of light incident to the eye (E, centre of the entrance pupil of the eye)enlarge picture
Fig. R2 Rays of light incident to the eye (E, centre of the entrance pupil of the eye)

Table R1 Differences between the sine and the tangent values of various angles (in degrees and radians). The error is calculated between the sine value and the value in radians and between the value in radians and the tangent value
angle (deg)angle (rad)sine
tangent valueerror (%) sine errorerror (%) tangent error
0.50.008 7270.008 7270.008 7270.000.00
10.017 4530.017 4520.017 4550.010.01
20.034 9070.034 8990.034 9210.020.04
30.052 3600.052 3360.052 4080.050.09
40.069 8130.069 7560.069 9270.080.16
50.087 2660.087 1560.087 4890.130.25
60.104 7200.104 5280.105 1040.180.37
70.122 1730.121 8690.122 7850.250.50
80.139 6260.139 1730.140 5410.330.65
100.174 5330.173 6480.176 3270.511.03
150.261 7990.258 8190.267 9491.152.35
5200.349 0660.342 0200.363 9702.064.27
300.523 5990.500 0000.577 3504.7210.27
References in periodicals archive ?
The refractive index of each lens was required to calculate the front and rear principal planes (Fig.
2] d lens thickness n refractive index Principal planes (VH): Front: [V.