Entrance pupil

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For the part of the eye, see pupil.

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).

The entrance pupil is the image of the aperture stop in the optics that come before it. In a camera, the aperture stop is the diaphragm aperture in the camera that the photographer adjusts to change the f-number. Opening the diaphragm wider increases the size of the pupil, allowing more light to reach the film.

The entrance pupil of the 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.^[1]

[edit] See also

• Aperture stop
• Exit pupil
• f-number

[edit] References

1. ^ *Hecht, Eugene (1987). Optics, 2nd ed., Addison Wesley. ISBN 0-201-11609-X.

[edit] External links

• The Grid — Method for a precise location of the entrance pupil on a DSLR camera