noun
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.
このレンズの開放値はF2.8です。
The f-number of this lens is F2.8.
開放値が小さいほど、背景がぼけやすくなります。
The smaller the f-number, the easier it is to blur the background.
F値 is a more common and general term for f-number, often used in everyday photography contexts. 開放値 is more technical and may emphasize the maximum aperture or the numerical ratio.
Compound of 開放 (かいほう, 'open, aperture') and 値 (ち, 'value, numerical value'). The term directly translates to 'aperture value'.