Topic summary
Cone of rays
Extracted from the Wikipedia article Aperture.
In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. The aperture defines a set of rays from each point on an object that will come to a focus in the image plane. This set of rays, sometimes called a bundle of rays or cone of rays, is mathematically a generalized cone (or a bundle of half-lines).