Entrance pupil

Entrance pupil
For the part of the eye, see Pupil.
A camera lens adjusted for large and small aperture. The entrance pupil is the image of the physical aperture, as seen through the front of the lens. The size and location may differ from those of the physical aperture, due to magnification by the lens.
The apparent location of the anatomical pupil of a human eye (black circle) is the eye's entrance pupil. The outside world appears to be seen from the point at the center of the entrance pupil. (The pupil itself, which lens designers would call the aperture, is in a slightly different location because the image is magnified by the cornea.)

In an optical system, the entrance pupil is the optical image of the physical aperture stop, as 'seen' through the front of the lens system. The corresponding image of the aperture as seen through the back of the lens system is called the exit pupil. If there is no lens in front of the aperture (as in a pinhole camera), the entrance pupil's location and size are identical to those of the aperture. Optical elements in front of the aperture will produce a magnified or minified image that is displaced from the location of the physical aperture. The entrance pupil is usually a virtual image: it lies behind the first optical surface of the system.

The geometric location of the entrance pupil is the vertex of the camera's angle of view[1] and consequently its center of perspective, perspective point, view point, projection centre[2] or no-parallax point.[3] This point is important in panoramic photography, because the camera must be rotated around it in order to avoid parallax errors in the final, stitched panorama.[4][5] Depending on the lens design, the entrance pupil location on the optical axis may be behind, within or in front of the lens system; and even at infinite distance from the lens in the case of telecentric systems.

In photography, the size of the entrance pupil (rather than the size of the physical aperture itself) is used to calibrate the opening and closing of the diaphragm aperture. The f-number ("relative aperture"), N, is defined by N = f/EN, where f is the focal length and EN is the diameter of the entrance pupil.[6] Increasing the focal length of a lens (i.e., zooming in) will usually cause the f-number to increase, and the entrance pupil location to move further back along the optical axis.

The entrance pupil of the human eye, which is not quite the same as the physical pupil, is typically about 4 mm in diameter. It can range from 2 mm (f/8.3) in a very brightly lit place to 8 mm (f/2.1) in the dark.[7]


See also

References

  1. ^ Greivenkamp, John E. (2004). Field Guide to Geometrical Optics. SPIE Field Guides vol. FG01. Bellingham, Wash: SPIE. p. 27. ISBN 9780819452948. OCLC 53896720. http://spie.org/x32310.xml. 
  2. ^ Lenhardt, Karl (pdf). Optical Measurement Techniques with Telecentric Lenses. http://www.schneiderkreuznach.com/pdf/div/optical_measurement_techniques_with_telecentric_lenses.pdf. Retrieved Aug. 14, 2009. 
  3. ^ Littlefield, Rik (Feb. 6, 2006) (pdf). Theory of the “No-Parallax” Point in Panorama Photography. ver. 1.0. http://www.janrik.net/PanoPostings/NoParallaxPoint/TheoryOfTheNoParallaxPoint.pdf. Retrieved Jan. 14, 2007. 
  4. ^ Kerr, Douglas A. (2005). "The Proper Pivot Point for Panoramic Photography" (PDF). The Pumpkin. Archived from the original on Apr. 7, 2008. http://web.archive.org/web/20080407174910/http://doug.kerr.home.att.net/pumpkin/Pivot_Point.pdf. Retrieved Jan. 14, 2007. 
  5. ^ van Walree, Paul. "Misconceptions in photographic optics". http://toothwalker.org/optics/misconceptions.html#m6. Retrieved Jan. 14, 2007.  Item #6.
  6. ^ Jacobson, Ralph (et al.) (1988). The Manual of Photography (8th ed.). Focal Press. ISBN 0-240-51268-5.  p.49
  7. ^ Hecht, Eugene (1987). Optics (2nd ed.). Addison Wesley. ISBN 0-201-11609-X. 

External links

  • Stops and Pupils in Field Guide to Geometrical Optics Greivenkamp, John E, 2004

Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • entrance pupil — noun : the stop in an optical instrument or the virtual image of the stop that determines the angular diameter of the bundle of rays traversing the instrument from a given point in the object space compare exit pupil * * * Optics. the image of… …   Useful english dictionary

  • entrance pupil — Optics. the image of the aperture viewed from the objective of an optical system limiting the rays that enter the system. Cf. exit pupil. * * * …   Universalium

  • pupil — pupil1 pupilless, adj. /pyooh peuhl/, n. 1. a person, usually young, who is learning under the close supervision of a teacher at school, a private tutor, or the like; student. 2. Civil Law. an orphaned or emancipated minor under the care of a… …   Universalium

  • Pupil — The pupil is the hole that is located in the center of the iris of the eye and that controls the amount of light that enters the eye.Cassin, B. and Solomon, S. Dictionary of Eye Terminology . Gainsville, Florida: Triad Publishing Company, 1990.]… …   Wikipedia

  • Pupil (disambiguation) — The pupil is the variable sized, black circular opening in the centre of the iris.Pupil may also refer to:*Pupil, another term for a student *Pupil (band), a Filipino rock band *Pupil, a trainee Barrister (England and Wales) *The terms Entrance… …   Wikipedia

  • Pupil magnification — The pupil magnification of an optical system is the ratio of the diameter of the exit pupil to the diameter of the entrance pupil. The pupil magnification is used in calculations of exposure. For all symmetric lenses, and for many conventional… …   Wikipedia

  • Exit pupil — In optics, the exit pupil is a virtual aperture in an optical system. Only rays which pass through this virtual aperture can exit the system. The exit pupil is the image of the aperture stop in the optics that follow it. In a telescope or… …   Wikipedia

  • exit pupil — noun : the image of the entrance pupil of an optical system viewed from the image space (as at the eyepiece) * * * Optics. the ridge of the entrance pupil of an optical system, indicating the place where the pupil of the eye should be placed to… …   Useful english dictionary

  • exit pupil — Optics. the ridge of the entrance pupil of an optical system, indicating the place where the pupil of the eye should be placed to view the object. Also called eye point. * * * …   Universalium

  • Common Entrance Examination — Common Entrance Examinations (commonly known as CE) are taken by some children in the UK as part of the admissions process for academically selective secondary schools at age 13 or (for girls) 11. Most of the secondary schools that use Common… …   Wikipedia

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”