# focus, foci +

#### (Latin: hearth, fireplace; fire, flame; central point, center)

The word "focus" was introduced into mathematics by Johannes Kepler in 1604 with the meaning of any "central point".

autofocus
Having the ability to focus automatically; such as, an autofocus lens or an autofocus camera.
bifocal
1. Having two focal lengths.
2. Having one section that corrects for distant vision and another that corrects for near vision, as an eyeglass lens.
3. Embodying two distinct and often conflicting goals, interests, or courses of action.

Bibocals are eyeglasses made with double lenses of different focuses so that the wearer may have one focus for distant vision and one of close focus for reading.

bifocal lens
A lens used in cases of presbyopia, in which one portion is suited for distant vision, the other for reading and close work in general.

The reading addition may be cemented to the lens, fused to the front surface, or ground into a one-piece form; other bifocal lenses are the flat-top Franklin type, or blended invisible.

bifocals
Eye glasses with lenses that are divided into two parts.

The upper half is for looking at things far away and the lower half is for reading or for looking at things that are near.

electrofocusing, isoelectric focusing
1. A protein separation technique in which a mixture of protein molecules is resolved into its components by subjecting the mixture to an electric field in a supporting gel having a previously established pH gradient.
2. An electrophoretic technique for separating proteins by causing them to migrate under the influence of an electric field through a medium; such as, a gel, having a pH gradient to locations with pH values corresponding to their isoelectric points.
3. Electrophoresis in which a pH gradient is established in a gel medium and proteins migrate until they reach the site, or focus, at which the pH is equal to their isoelectric point.
4. A variation of the electrophoretic separation technique or a movement of small suspended particles or very large molecules in a liquid driven by an electrical potential difference.

The separation of molecules occurs in a combination of potential and pH gradients resulting in sharper separations compared to simple electrophoresis.

electromagnetic focusing
1. A method of adjusting the electron beam in a television picture tube by varying the direct current flowing through the coils attached to the tube, and so, altering or changing the surrounding magnetic field.
2. Focusing the electron beam in a television picture tube by means of a magnetic field parallel to the beam.

The field is produced by sending an adjustable value of direct current through a focusing coil mounted on the neck of the tube.

electrostatic focus
1. In television picture tubes, a technique of directing an electron beam in a cathode-ray tube by changing the voltage applied to the focusing electrode.
2. The production of a focused electron beam in a cathode-ray tube with the application of an electric field.
electrostatic focusing
1. The focusing of an electron beam by the action of an electric field.
2. A method of focusing the cathode-ray beam to a fine spot by the application of electrostatic potentials to one or more elements of an electron lens system.
3. A method of focusing an electron beam by the action of an electric field, as in the electron gun of a cathode-ray tube, so that the beam will have the required small area on a screen or other surface.
epifocal (ep" i FOH k'l)
Located or occurring at the point on the earth's surface directly above the focus epicenter of an earthquake or underground nuclear explosion.
foci
1. Plural of focus.
2. The origin or center of a disseminated disease.
focimeter
A device for measuring the dioptic strength of a lens.
focus
1. 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.
2. The distinctness or clarity of an image rendered by an optical system.
3. The state of maximum distinctness or clarity of an image; such as, in focus, out of focus.
4. An apparatus used to adjust the focal length of an optical system in order to make an image distinct or clear; for an example, a camera with automatic focus.
5. A center of interest or activity.
6. Close or narrow attention; concentration.
7. A condition in which something can be clearly apprehended or perceived: "He simply couldn't get the problem into focus."
8. In pathology, the region of a localized bodily infection or disease.
9. In geology, the point of origin of an earthquake.
10. Etymology: from New Latin, focus, "central point"; from Latin focus, "hearth, fireplace".

The New Latin use was introduced in a Latin text about astronomy in 1604 by the German astronomer and mathematician, Johann Kepler, with reference to the "burning point (at which heat rays meet) of a lens or mirror".

focused electrode
The electrode that controls the convergence of the electron beam and permits focusing the spot on the screen of a cathode ray tube.
focusing
1. The concentration of attention or energy on something.
2. The act of bringing into focus or converging at a point.
3. The change in strength of the crystalline lens of the eye that permits clear vision to be achieved at various distances.
focusing collector
A device that focuses solar radiation on a surface or point.

Cross references of word groups that are related, directly, indirectly, or partly to: "fire, burn, glow, or ashes": ars-, ard-; -bust; cand-, cend-; caust-, caut-; crema-; ciner-; ether-; flagr-; flam-; fulg-; gehenna-; ign-; phleg-; phlog-; pyreto-, -pyrexia; pyr-; spod- (ashes; waste); volcan-.