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Words related to focal

fo·cal
F f

  • focal length

    the distance from a focal point of a lens or mirror to the corresponding principal plane. Symbol: f.

  • f-number

    a number corresponding to the ratio of the focal length to the diameter of a lens system, especially a camera lens. In f /1.4, 1.4 is the f-number and signifies that the focal length of the lens is 1.4 times as great as the diameter. /, f/, f, f: Abbreviation: f.

  • astronomical telescope

    any telescope designed and mounted for use in astronomy. Such telescopes usually form inverted images

  • compound microscope

    an instrument for magnifying small objects, consisting of a lens of short focal length for forming an image that is further magnified by a second lens of longer focal length

  • focal plane

    a plane through a focal point and normal to the axis of a lens, mirror, or other optical system. Compare principal plane.

  • focal point

    Also called principal focus. Optics. either of two points on the axis of a mirror, lens, or other optical system, one point being such that rays diverging from it are deviated parallel to the axis upon refraction or reflection by the system and the other point being such that rays parallel to the axis of the system converge to the point upon refraction or reflection by the system.
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