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.

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.

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.

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.