focus, in optics, the point at which rays converge after reflection by a concave mirror or refraction by a convex lens , also known as a real focus. The point from which rays appear to diverge after reflection by a convex mirror or refraction by a concave lens is known as a virtual focus. See image .
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
See more Encyclopedia articles on: Physics