key: aprtr

type: f

  1. f: the f-number


The f-number is the ratio of the focal length to the diameter of the aperture. When photographers write ``f/5.6'' that means the diameter of the aperture is the focal length over 5.6; 5.6 is the f-number.

In real cameras with complicated lenses, the ``effective aperture'' is taken to be the region on the front of the lens through which light rays can get to the film. This is also called the ``entrance pupil.'' This is the aperture that the aprtr chunk is meant to specify.

If the aperture is not circular, then its area should be equal to the area of a circle of this diameter.


This chunk only makes sense inside a camera chunk.


See the camera example .