Assertion: lens's aperture | /r/HasProperty | specified as f-number
Facets:
Source sentences:
text: The maximum usable aperture of a lens is specified as the focal ratio or f-number, defined as the lens's focal length divided by the effective aperture (or entrance pupil), a dimensionless number.
text: The relative aperture is specified as an f-number, the ratio of the lens focal length to its effective aperture diameter.