To concentrate Attention or Effort
R E F E R E N C E S
It is impossible [in photography] to focus all points of a three-dimensional scene on the film at the same time, but a satisfactory sharpness can usually be achieved over a considerable depth of the scene.
Adjustment is most critical when focusing on a nearby object with wide-open lens. It is least critical for a distant object with the smallest lens opening. The accuracy of the focusing may be judged by observing the sharpness of the image on a translucent glass surface in reflect-type cameras or by superimposing two images in a rangefinder in some other cameras.
[Light and Color, by Clarence Rainwater, Prof. of Physics, San Francisco State College, Original Project Editor Herbert S. Zim, Golden Press, NY, Western Publishing Company, Inc., 1971. p. 81]
R E F E R E N C E S
1 Focus n [NL, fr. L. hearth] [1644] 1a: a point at which rays [as of light, heat, or sound] converge or from which they diverge or appear to diverge; specif: the point where the geometrical lines or their prolongations conforming to the rays diverging from or converging toward another point intersect and give rise to an image after reflection by a mirror or refraction by a lens or optical system b: a point of convergence of a beam of particles [as electrons] 2a: Focal Length b: adjustment [for distinct vision; also: the area that may be seen distinctly or resolved into a clear image c: a state or condition permitting clear perception or understanding [tried to bring the issues into __] d: Direction 6c a comic section 4: a localized area of disease or the chief site of a generalized disease or infection 5a: a center of activity, attraction, or attention [the __ of the meeting was drug abuse] b: a point of concentration 6: the place or origin of an earthquake or moonquake 7: directed attention: Emphasis -in focus: having or giving the proper sharpness of outline due to good focusing -out of focus: not in focus
2 Focus vt [1775] 1a: to bring into focus b: to adjust the focus of [as the eye or a lens] 3: to cause to be concentrated [__ed their attention on the most urgent problems] 3: to bring [as light rays] to a focus: concentrate -vi 1: to come to a focus: Converge 2: to adjust oneÍs eye or a camera to a particular range 3: to concentrate attention or effort
[Merriam-Webster's Collegiate Dictionary, 10th Edition. Springfield, MA, USA: Merriam-Webster, Inc. 1995.]
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