f-stop
The
photographer adjusts the opening of the aperture by setting the f-stop. An
f-stop is a ratio of the focal length of the lens to the diameter of the
opening of the aperture. For example, a 50 mm lens with an aperture opened up
to a diameter of 12.5 mm results in an f-stop of f4 (50 ÷ 12.5 = 4).
