Focus on Light

Focus (optics)

In geometrical optics, a focus, also called an image point, is a point where light rays originating from a point on an object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics. Even in the absence of aberrations, the smallest possible blur circle is the Airy disc caused by diffraction from the optical system's aperture; diffraction is the ultimate limit to the light focusing ability of any optical system. Aberrations tend to worsen as the aperture diameter increases, while the Airy circle is smallest for large apertures.

Light

Light, visible light, or visible radiation is electromagnetic radiation that can be perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400–700 nanometers (nm), corresponding to frequencies of 750–420 terahertz. The visible band sits adjacent to the infrared and the ultraviolet, called collectively optical radiation.

focus

Noun

1. A point at which reflected or refracted rays of light converge.
2. A point of a conic at which rays reflected from a curve or surface converge.

Verb

1. To cause (rays of light, etc) to converge at a single point.
2. To adjust (a lens, an optical instrument) in order to position an image with respect to the focal plane.

light

Noun

1. Electromagnetic radiation in the wavelength range visible to the human eye (about 400–750 nanometers): visible light.
2. Electromagnetic radiation in the wavelength range visible to the human eye or in nearby ranges (infrared or ultraviolet radiation).

Verb

1. To start (a fire).
2. To set fire to; to set burning.