Focus Point

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.

Focus (geometry)

In geometry, focuses or foci are special points with reference to which any of a variety of curves is constructed. For example, one or two foci can be used in defining conic sections, the four types of which are the circle, ellipse, parabola, and hyperbola. In addition, two foci are used to define the Cassini oval and the Cartesian oval, and more than two foci are used in defining an n-ellipse.

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.

point

Noun

1. A small dot or mark.

Interjection

1. Point taken; understood; got it.