Focal length
(Redirected from Focal Length)
The focal length of a lens is the distance from the lens to the point at which parallel incident light converges. For example, since the rays from the sun are effectively parallel, a magnifying glass can be used to produce an intense spot at a distance equal to the focal length.
For a diverging (concave) lens, the focus is virtual : it is the distance behind the lens from which incident parallel light appears to emanate.