f-stop
The aperture expressed as the ratio of focal length to the diameter of the entrance pupil.
Also written
f numberfstop
Because it is a ratio, f/4 admits the same light per unit area on any lens, which is what makes exposure settings portable between them. Each full stop — f/2.8, f/4, f/5.6, f/8 — halves the light. The counter-intuitive part is that a larger number is a smaller opening.
Nearby in Photography
- dynamic range — The span between the darkest and brightest tones a sensor can record in one exposure.
- exposure compensation — A deliberate offset applied to the camera's metered exposure.
- focal length — The optical property, in millimetres, that determines a lens's angle of view and magnification.
- full frame — A sensor the size of a 35mm film frame, around 36 by 24 millimetres.