focal point

The central point of the focal plane that lies on the optical axis, one focal length away from the lens. A lens or lens system typically has a front focal point (the first focal point in the direction of light travel) and a back focal point on the opposite side.

Synonyms: focus

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Geometrical Construction of Ray Diagrams

A popular method of representing a train of propagating light waves involves the application of geometrical optics to determine the size and location of images formed by a lens or multi-lens system. This tutorial explores how two representative light rays can establish the parameters of an imaging scenario.