aperture ratio
Technical term used in optics, photography, and display engineering to describe the ratio of the effective opening area to the total area.
The aperture ratio of this lens is F2.8.
The higher the aperture ratio of an LCD panel, the brighter the screen.
F-number is the reciprocal of the relative aperture; 開口率 is often expressed as a ratio like 1:2.8.
Compound of 開口 (opening, aperture) and 率 (rate, ratio). A straightforward technical coinage.