principal pointn.

Brit.

/ˌprɪnsᵻpl ˈpɔɪnt/, U.S.

/ˈˌprɪnsəp(ə)l ˈpɔɪnt/

Forms: see principal adj., n., and adv. and point n.¹

Origin: Formed within English, by compounding. Etymons: principal adj., point n.¹

Etymology: < principal adj. + point n.¹ In sense 1 after Middle French principal poinct (1558 in the passage translated in quot. 1591). In sense 3 after German Hauptpunkt ( C. F. Gauss Dioptrische Untersuchungen (1841) vii. 13); compare French point principal (1851 or earlier in this sense).

†1. Astronomy and Astrology. Each of the two equinoctial and two solstitial points of the ecliptic. Obsolete.

ΚΠ

1591 F. Sparry tr. C. de Cattan Geomancie i. xxviii. 41 The principall pointes [Fr. principaux poincts]..do diuide the Zodiacke into foure partes or quarters, responding to the foure parts and seasons of the yeare.

1594 T. Blundeville Exercises ii. i. xvi. f. 149^v The two Equinoxes, and the two Solstices, are commonlie called the foure cardinall or principall pointes.

2. Perspective. The point where the principal ray meets the picture plane.

ΘΚΠ

society > leisure > the arts > visual arts > painting and drawing > perspective > [noun] > planes, lines, or points

horizontal plane1638

eye-pointa1650

table1670

principal point1671

plan1678

geometrical plane1695

terrestrial line1704

vertical plane1704

baseline1724

station line1724

middle ground1753

picture plane1771

middle distance1778

primitive plane1798

seat1815

mid-distance1828

ground-plane1833

station point1859

mid-ground1864

no-sky line1927

1671 Philos. Trans. (Royal Soc.) 6 3047 By Glasses of an hyperbolical figure, the rays, coming from the principal point of the object to the Eye, would more exactly meet in one point at the bottom of the Retina.

1686 R. Blome Gentlemans Recreation vi. 181/2 The other kind of Perspective..designs by a principal Point, from whence all Parallels to that Principal do meet in that Point.

1713 E. Wells Young Gentleman's Opticks iv. 160 All right Lines, which are perpendicular to the Picture, have the principal Point for their accidental Point.

1728 E. Chambers Cycl. at Distance Point of Distance, in Perspective, is a Point in the Horizontal Line at such Distance from the principal Point, as is that of the Eye from the same.

a1764 J. Harris Treat. Optics (1775) iii. 211 The picture ought always to be nearly at right angles to the axis passing through the principal point in it.

1997 Renaissance Q. 50 1175 In this diagram the proposed foreshortened image is a trapezoid, bcfg, which extends up toward a theoretical principal point on the right that would become apparent if you took a ruler and extended lines cf and bg until they met at a point.

3. Optics. Each of the two points at which the optic axis of a lens intersects the principal planes.In the case where the medium is the same on both sides of the lens, these points coincide with the nodal points, which have the property that the straight line between the first of these and any point of the object is parallel to that between the second and the corresponding point of the image.

ΚΠ

1887 R. S. Heath Treat. Geom. Optics v. 87 These two planes are called the principal planes and the points where they cut the axis principal points.

1911 Encycl. Brit. XVI. 423/1 In the special case when the initial and final medium is the same, as for example, a lens in air, we have f = −f′, and the nodal points coincide with the principal points of the system.

2002 M. P. Keating Geom., Physical, & Visual Optics (ed. 2) xv. 297/2 The point at which the optical axis passes through H₁ [sc. the primary principal plane], is called the primary principal point.

This entry has been updated (OED Third Edition, June 2007; most recently modified version published online March 2022).

单词	principal point
释义	principal pointn. Brit. /ˌprɪnsᵻpl ˈpɔɪnt/, U.S. /ˈˌprɪnsəp(ə)l ˈpɔɪnt/ Forms: see principal adj., n., and adv. and point n.¹ Origin: Formed within English, by compounding. Etymons: principal adj., point n.¹ Etymology: < principal adj. + point n.¹ In sense 1 after Middle French principal poinct (1558 in the passage translated in quot. 1591). In sense 3 after German Hauptpunkt ( C. F. Gauss Dioptrische Untersuchungen (1841) vii. 13); compare French point principal (1851 or earlier in this sense). †1. Astronomy and Astrology. Each of the two equinoctial and two solstitial points of the ecliptic. Obsolete. ΚΠ 1591 F. Sparry tr. C. de Cattan Geomancie i. xxviii. 41 The principall pointes [Fr. principaux poincts]..do diuide the Zodiacke into foure partes or quarters, responding to the foure parts and seasons of the yeare. 1594 T. Blundeville Exercises ii. i. xvi. f. 149^v The two Equinoxes, and the two Solstices, are commonlie called the foure cardinall or principall pointes. 2. Perspective. The point where the principal ray meets the picture plane. ΘΚΠ society > leisure > the arts > visual arts > painting and drawing > perspective > [noun] > planes, lines, or points horizontal plane1638 eye-pointa1650 table1670 principal point1671 plan1678 geometrical plane1695 terrestrial line1704 vertical plane1704 baseline1724 station line1724 middle ground1753 picture plane1771 middle distance1778 primitive plane1798 seat1815 mid-distance1828 ground-plane1833 station point1859 mid-ground1864 no-sky line1927 1671 Philos. Trans. (Royal Soc.) 6 3047 By Glasses of an hyperbolical figure, the rays, coming from the principal point of the object to the Eye, would more exactly meet in one point at the bottom of the Retina. 1686 R. Blome Gentlemans Recreation vi. 181/2 The other kind of Perspective..designs by a principal Point, from whence all Parallels to that Principal do meet in that Point. 1713 E. Wells Young Gentleman's Opticks iv. 160 All right Lines, which are perpendicular to the Picture, have the principal Point for their accidental Point. 1728 E. Chambers Cycl. at Distance Point of Distance, in Perspective, is a Point in the Horizontal Line at such Distance from the principal Point, as is that of the Eye from the same. a1764 J. Harris Treat. Optics (1775) iii. 211 The picture ought always to be nearly at right angles to the axis passing through the principal point in it. 1997 Renaissance Q. 50 1175 In this diagram the proposed foreshortened image is a trapezoid, bcfg, which extends up toward a theoretical principal point on the right that would become apparent if you took a ruler and extended lines cf and bg until they met at a point. 3. Optics. Each of the two points at which the optic axis of a lens intersects the principal planes.In the case where the medium is the same on both sides of the lens, these points coincide with the nodal points, which have the property that the straight line between the first of these and any point of the object is parallel to that between the second and the corresponding point of the image. ΚΠ 1887 R. S. Heath Treat. Geom. Optics v. 87 These two planes are called the principal planes and the points where they cut the axis principal points. 1911 Encycl. Brit. XVI. 423/1 In the special case when the initial and final medium is the same, as for example, a lens in air, we have f = −f′, and the nodal points coincide with the principal points of the system. 2002 M. P. Keating Geom., Physical, & Visual Optics (ed. 2) xv. 297/2 The point at which the optical axis passes through H₁ [sc. the primary principal plane], is called the primary principal point. This entry has been updated (OED Third Edition, June 2007; most recently modified version published online March 2022). < n.1591
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