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  2. f-number - Wikipedia

    en.wikipedia.org/wiki/F-number

    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]

  3. Focal length - Wikipedia

    en.wikipedia.org/wiki/Focal_length

    The rear focal length f ′ is the distance from the rear principal plane H ′ to the rear focal point F ′. Front focal distance (FFD) The front focal distance (FFD) (s F) is the distance from the front focal point of the system (F) to the vertex of the first optical surface (S 1). [1] [3] Some authors refer to this as "front focal length".

  4. Focus (optics) - Wikipedia

    en.wikipedia.org/wiki/Focus_(optics)

    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.

  5. Lens - Wikipedia

    en.wikipedia.org/wiki/Lens

    The right figure shows how the image of an object point can be found by using three rays; the first ray parallelly incident on the lens and refracted toward the second focal point of it, the second ray crossing the optical center of the lens (so its direction does not change), and the third ray toward the first focal point and refracted to the ...

  6. Conjugate points - Wikipedia

    en.wikipedia.org/wiki/Conjugate_points

    In differential geometry, conjugate points or focal points [1] [2] are, roughly, points that can almost be joined by a 1-parameter family of geodesics. For example, on a sphere, the north-pole and south-pole are connected by any meridian. Another viewpoint is that conjugate points tell when the geodesics fail to be length-minimizing.

  7. A Dictionary of Modern English Usage - Wikipedia

    en.wikipedia.org/wiki/A_Dictionary_of_Modern...

    The 1996 third edition was re-titled as The New Fowler's Modern English Usage, and revised in 2004, was mostly rewritten by Robert W. Burchfield, as a usage dictionary that incorporated corpus linguistics data; [1] and the 2015 fourth edition, revised and re-titled Fowler's Dictionary of Modern English Usage, was edited by Jeremy Butterfield ...

  8. Thesis statement - Wikipedia

    en.wikipedia.org/wiki/Thesis_statement

    A thesis statement is a statement of one's core argument, the main idea(s), and/or a concise summary of an essay, research paper, etc. [1] It is usually expressed in one or two sentences near the beginning of a paper, and may be reiterated elsewhere, such as in the conclusion.

  9. Focal point (game theory) - Wikipedia

    en.wikipedia.org/wiki/Focal_point_(game_theory)

    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 ]