Assertion: focal ratio | /r/HasProperty | divided by the aperture
Facets:
Source sentences:
text: The focal ratio of a telescope is simply the focal length divided by the aperture (making sure both measurements are in the same units - focal lengths are usually given in millimeters, but apertures are often given in inches).
text: Before leaving the topic of the objective lens, I think I should bring up the subject of focal ratio - the focal length (distance from the objective to the focus point) divided by the aperture (diameter).
text: A scope's focal ratio is the focal length divided by the aperture; for instance a 100-millimeter refractor with a focal length of 600 millimeters has a focal ratio of f/6.