An Etymological Dictionary of Astronomy and Astrophysics

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فرهنگ ریشه‌شناختی اخترشناسی-اخترفیزیک

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aperture ratio
  وابر ِ دهانه  
vâbar-e dahâné
Fr.: rapport d'ouverture  

The ratio of the effective diameter of a lens or mirror to its focal length.

See also: → aperture; → ratio.