focus

Definitions

General English

  • noun a point where rays of light from an object meet
  • noun a point where the details of the photograph are clear and sharp
  • noun the centre of attention
  • verb to change something so as to be able to see clearly
  • noun a point which everything is focused on.

General Science

  • verb to direct something towards a particular point or purpose

Aviation

  • verb to make things such as light rays converge on a central point
  • verb to give an object or image a clear outline or detail by adjustment of an optical device

Computing

  • noun a particular window or field that is currently ready to accept a user’s command
  • verb to adjust a monitor so that the image that is displayed on the screen is sharp and clear

Electronics

  • 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.
  • synonymfocal point

Information & Library Science

  • verb to concentrate one’s attention on something

Media Studies

  • noun a device on a camera for adjusting the lens so that the image is clear

Medical

  • noun the centre of an infection
  • verb to adjust a lens until an image is clear and sharp

Sports

  • noun concentrated effort or attention on a particular thing
  • noun the aim of something, e.g. a fitness programme or a competitive tactic

Origin & History of “focus”

Latin focus meant ‘fireplace’, and in post-classical times it came to be used for ‘fire’ itself – hence French feu, Italian fuoco, Spanish fuego, all meaning ‘fire’, and hence too the English derivatives fuel and fusillade. The first writer known to have used it in its modern sense ‘point of convergence’ was the German astronomer Johannes Kepler, in 1604, but the reason for his choice of word is not clear. It may have been some metaphorical notion of the ‘hearth’ symbolizing the ‘centre of the home’, but it has also been suggested that it may have been preceded and inspired by the use of focus for the ‘burning point’ of a mirror (not actually recorded until somewhat later). The philosopher Thomas Hobbes appears to have introduced the term into English, in 1656.

A medieval Latin derivative of focus was focārius, from which French got foyer ‘hearth, home’, borrowed by English in the 19th century for a public entrance hall or lobby.
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