Optics
F-Number (f-stop)
The f-number (or f-stop) is the ratio of focal length to aperture diameter. Lower f-numbers mean larger apertures and more light gathering.
Variables
f/\#unitless
F-number
fm
Focal length
Dm
Aperture diameter
Your notes
0/5000
Common questions
What is the F-Number (f-stop) formula?
F-Number (f-stop) is written f/\# = f/D. The f-number (or f-stop) is the ratio of focal length to aperture diameter. Lower f-numbers mean larger apertures and more light gathering. It belongs to Optics, under Optical Instruments.
What are the units in f/\# = f/D?
In SI units, f/\# is f-number (dimensionless); f is focal length, measured in m; D is aperture diameter, measured in m.