Entrance pupil
In an
The entrance pupil is a useful concept for determining the size of the cone of rays that an optical system will accept. Once the size and the location of the entrance pupil of an optical system is determined, the maximum cone of rays that the system will accept from a given object plane is determined solely by the size of the entrance pupil and its distance from the object plane, without any need to consider ray refraction by the optics.[1]
In photography, the size of the entrance pupil (rather than the size of the physical aperture stop) 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.[2] 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 center of the entrance pupil is the
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.[8]
Most optical systems are designed with a single aperture stop, and therefore have a single entrance pupil. In some cases, however, different elements serve as the aperture stop for objects at different distances.[1] In such cases, the system will have different entrance pupils for different object planes. Similarly, vignetting can cause different lateral locations at a given object plane to have different aperture stops, and therefore different entrance pupils.[1]
See also
References
- ^ ISBN 978-1-292-09693-3.
- ISBN 0-240-51268-5. p.49
- OCLC 53896720.
- ^ Lenhardt, Karl. "Optical Measurement Techniques with Telecentric Lenses" (PDF). Schneider Kreuznach. Archived from the original (PDF) on September 24, 2015. Retrieved Oct 14, 2014.
- ^ Littlefield, Rik (Feb 6, 2006). "Theory of the "No-Parallax" Point in Panorama Photography" (PDF). ver. 1.0. Retrieved Jan 14, 2007.
- ^ Kerr, Douglas A. (2005). "The Proper Pivot Point for Panoramic Photography" (PDF). The Pumpkin. Archived from the original (PDF) on Apr 7, 2008. Retrieved Jan 14, 2007.
- ^ van Walree, Paul. "Misconceptions in photographic optics". Archived from the original on April 19, 2015. Retrieved Jan 14, 2007. Item #6.
- ISBN 0-201-11609-X.
External links
- Stops and Pupils in Field Guide to Geometrical Optics Greivenkamp, John E, 2004
- Entrance and exit pupil, RP Photonics Encyclopedia