開かい放ほう値ち

noun

f-number; f-stop; focal ratio

Technical term used in photography and optics to describe the ratio of the lens's focal length to the diameter of the entrance pupil. Often seen in specifications and discussions about aperture.

• このレンズの開かい放ほう値ちはF2.8です。

  The f-number of this lens is F2.8.

• 開かい放ほう値ちが小ちいさいほど、背はい景けいがぼけやすくなります。

  The smaller the f-number, the easier it is to blur the background.