- To make light rays, a beam of radiation, energy, or particles converge. For instance, to make an electron beam converge properly on the screen of a CRT. Also called focusing (1).
- To make an adjustment which improves the sharpness of an image. Also, to adjust until the sharpest possible image is obtained. For example, to adjust a camera lens to achieve this effect. Also called focusing (2).
- In an optical system, such as a lens or a mirror, a point towards which an incident bundle of parallel rays of light converge. Also called focal point.
- In a geometric figure, such as an ellipse or hyperbola, a point which helps determine a conic section.
- synonym focal point
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