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A principal focus or focal point is a special focus: For a lens , or a spherical or parabolic mirror , it is a point onto which collimated light parallel to the axis is focused. Since light can pass through a lens in either direction, a lens has two focal points – one on each side.
Focal point may refer to: Focus (optics) Focus (geometry) Conjugate points, also called focal points; Focal point (game theory) Unicom Focal Point, a portfolio management software tool; Focal point review, a human resources process for employee evaluation; Focal Point, a 1976 studio album by McCoy Tyner "Focal Point: Mark of the Leaf", a Naruto ...
In game theory, a focal point (or Schelling point) is a solution that people tend to choose by default in the absence of communication in order to avoid coordination failure. [1] The concept was introduced by the American economist Thomas Schelling in his book The Strategy of Conflict (1960). [ 2 ]
A system is focal if an object ray parallel to the axis is conjugate to an image ray that intersects the optical axis. The intersection of the image ray with the optical axis is the focal point F ′ in image space. Focal systems also have an axial object point F such that any ray through F is conjugate to an image ray parallel to the optical axis.
The focal point F and focal length f of a positive (convex) lens, a negative (concave) lens, a concave mirror, and a convex mirror. The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power.
A conic is defined as the locus of points for each of which the distance to the focus divided by the distance to the directrix is a fixed positive constant, called the eccentricity e. If 0 < e < 1 the conic is an ellipse, if e = 1 the conic is a parabola, and if e > 1 the conic is a hyperbola.
Thomas Sutton and George Dawson define focal range for what we now call hyperfocal distance: [2] Focal Range. In every lens there is, corresponding to a given apertal ratio (that is, the ratio of the diameter of the stop to the focal length), a certain distance of a near object from it, between which and infinity all objects are in equally good ...
The f-number N is given by: = where f is the focal length, and D is the diameter of the entrance pupil (effective aperture).It is customary to write f-numbers preceded by "f /", which forms a mathematical expression of the entrance pupil's diameter in terms of f and N. [1]