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  1. focal length

    • IPA[ˈfōkəl ˌleNGTH]

    美式

    • n.
      the distance between the center of a lens or curved mirror and its focus.;the equivalent distance in a compound lens or telescope.
    • noun: focal length, plural noun: focal lengths

    • 更多解釋

    英式

    • n.
      the distance between the centre of a lens or curved mirror and its focus.

    Oxford Dictionary