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 (adjective) (not comparable)
Descriptive of the ability to see or to focus automatically: Examples include an autofocus lens or an autofocus camera.
bifocal (s) (noun), bifocals (pl)
1. Eye glasses with lenses that are divided into two parts with one section that corrects for distant vision and another that corrects for near vision, as an eyeglass lens; in other words: 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 the viewer.
2. 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 (s) (noun), bifocal lenses (pl)
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 of a bifocal lens 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 invisibly.

electromagnetic focusing (s) (noun), electromagnetic focusings (pl)
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: The electromagnetic focusing field is produced by sending an adjustable value of direct currents through a focusing coil mounted on the neck of the tube.
electrostatic focus (s) (noun), electrostatic focuses (pl)
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 (s) (noun), electrostatic focusings (pl)
1. The point at which rays of light, heat, etc., meet, diverge, or seem to diverge after being reflected from a mirror, bent by a lens, etc.
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.
epifocal (noun), epifocals (pl)
Located or occurring at the point on the earth's surface directly above the focus epicenter of an earthquake or underground nuclear explosion.
focimeter (s) (noun), focimeters (pl)
A device for measuring the dioptic, or the refraction of light; especially, by the strength of a lens or lenses.
focus (s) (noun), foci (pl)
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 clarity of an image; such as, in focus or 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 condition in which something can be clearly apprehended or perceived: Harry simply couldn't get the problem into focus.
6. In pathology, the region of a localized bodily infection or disease.
7. In geology, the point of origin of an earthquake.
8. 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 (s) (noun), focused electrodes (pl)
The electrode that controls the convergence of the electron beam and permits focusing the spot on the screen of a cathode ray tube.
focusing (s) (noun), focusings (pl)
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 (s) (noun), focusing collectors (pl)
A device that focuses solar radiation on a surface or point of the earth.
ionic focusing, gas focusing (s) (noun); ionic focusings, gas focusings (pl)
A method of concentrating an electron beam by utilizing the residual gas in a tube: The beam electrons ionize the gas molecules, forming a core of positive ions along the path of the beam which attracts beam electrons and so makes the beam more compact resulting in ionic focusings and gas focusings.
matrifocal (s) (noun), matrifocals (pl)
1. Pertaining to, or designating a family unit or structure headed by the mother and lacking a father permanently or for extended periods.
2. Focused or centered on the mother.
multifocal (adjective), more multifocal, most multifocal
With reference to an eyeglass lens that has several focusing areas that correct for both nearsightedness and farsightedness.

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-.