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 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. 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. The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. )

In an optical system, the entrance pupil is a virtual aperture that defines the area at the entrance of the system that can accept light. Rays that pass through the pupil are able to enter the optical system and pass through it to the exit (neglecting vignetting). In Photography and Optics, vignetting is a reduction of an image's brightness or saturation at the Periphery compared to the image center

The entrance pupil is the image (usually virtual) of the aperture stop in the optics that come before it. In Optics, a virtual image is an image in which the outgoing rays from a point on the object never actually intersect at a point In a camera, the aperture stop is the diaphragm aperture in the camera that the photographer adjusts to control how much light reaches the film. A camera is a device used to capture images either as still Photographs or as sequences of moving images ( Movies or Videos. In Optics, a diaphragm is a thin opaque structure with an opening ( Aperture) at its centre The setting of the aperture is typically represented by the f-number, which is the ratio of the focal length of the lens to the diameter of the entrance pupil (not the diameter of the aperture itself). The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light.

The entrance pupil of the eye, which is not quite the same as the physical pupil, is typically about 4 mm in diameter. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain 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. It can range from 2 mm (f/8.3) in a very brightly lit place to 8 mm (f/2. 1) in the dark. ^[1]

Depending on the lens design, the entrance pupil may be located within the lens system, in front of it, or even at infinity in the case of telecentric systems. A telecentric lens is a compound lens with an unusual geometric property in how it forms images The location of the entrance pupil is important in panoramic photography, because the camera must be rotated about the centre of the entrance pupil to prevent parallax error when photographs are stitched together into a panorama. Panoramic photography is a format of Photography that aims to create images with exceptionally wide fields of view, but has also come to refer to any photograph that Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between Image stitching or photo stitching is the process of combining multiple Photographic Images with overlapping fields of view to produce a segmented Panorama ^{[2] [3]} As a result, the centre of the pupil is sometimes called the "no-parallax point" of the lens. ^[4]

See also

• Exit pupil
• Pupil magnification

References

1. ^ Hecht, Eugene (1987). In Optics, the exit pupil is a virtual Aperture in an optical system The pupil magnification of an optical system is the ratio of the diameter of the Exit pupil to the diameter of the Entrance pupil. Optics, 2nd ed. , Addison Wesley. ISBN 0-201-11609-X.  
2. ^ Kerr, Douglas A. (2005). The Proper Pivot Point for Panoramic Photography (PDF). The Pumpkin. Retrieved on 2007-01-14. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1129 - Formal approval of the Order of the Templar at the Council of Troyes.
3. ^ van Walree, Paul. Misconceptions in photographic optics. Retrieved on 2007-01-14. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1129 - Formal approval of the Order of the Templar at the Council of Troyes. Item #6.
4. ^ Littlefield, Rik (2006-02-06). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 46 BC - Julius Caesar defeats the combined army of Pompeian followers and Numidians under Metellus Scipio "Theory of the “No-Parallax” Point in Panorama Photography" (pdf). ver. 1. 0. Retrieved on 2007-01-14. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1129 - Formal approval of the Order of the Templar at the Council of Troyes.

External links

• The Grid — Alain Hamblenne's method for a precise location of the entrance pupil on a DSLR camera