|—n , pl -cuses, -ci|
|1.||a point of convergence of light or other electromagnetic radiation, particles, sound waves, etc, or a point from which they appear to diverge|
|2.||focal point another name for focal length|
|3.||optics the state of an optical image when it is distinct and clearly defined or the state of an instrument producing this image: the picture is in focus; the telescope is out of focus|
|4.||a point upon which attention, activity, etc, is directed or concentrated|
|5.||geometry a fixed reference point on the concave side of a conic section, used when defining its eccentricity|
|6.||Compare epicentre the point beneath the earth's surface at which an earthquake or underground nuclear explosion originates|
|7.||pathol the main site of an infection or a localized region of diseased tissue|
|—vb (often foll by on) , -cuses, -ci, -cuses, -cusing, -cused, -cusses, -cussing, -cussed|
|8.||to bring or come to a focus or into focus|
|9.||to fix attention (on); concentrate|
|[C17: via New Latin from Latin: hearth, fireplace]|
focus fo·cus (fō'kəs)
n. pl. fo·cus·es or fo·ci (-sī', -kī')
A point at which rays of light or other radiation converge or from which they appear to diverge, as after refraction or reflection in an optical system. Also called focal point.
See focal length.
The distinctness or clarity of an image rendered by an optical system.
The state of maximum distinctness or clarity of such an image.
An apparatus used to adjust the focal length of an optical system in order to make an image distinct or clear.
The region of a localized bodily infection or disease.
To cause light rays or other radiation to converge on or toward a central point; concentrate.
To adjust a lens or instrument to produce a clear image.
To converge on or toward a central point of focus; be focused.
|focus (fō'kəs) Pronunciation Key
Plural focuses or foci (fō'sī', fō'kī')
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