F = f / D
where f is the focal length, and D is the diameter of the entrance pupil (effective aperture).
status
not learned
measured difficulty
37% [default]
last interval [days]
repetition number in this series
0
memorised on
scheduled repetition
scheduled repetition interval
last repetition or drill
F-number - Wikipedia, the free encyclopedia tio in telescopes 6 Working f-number 7 History
7.1 Origins of relative aperture 7.2 Aperture numbering systems 7.3 Typographical standardization
8 See also 9 References 10 External links
Notation[edit]
The f-number N is given by:
<span>where is the focal length, and is the diameter of the entrance pupil (effective aperture). It is customary to write f-numbers preceded by f/, which forms a mathematical expression of the entrance pupil diameter in terms of f and N. [2] For example, if a lens's focal length is