f number

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f number

Designation for a photographic lens which gives the ratio of the focal length to the diameter of the effective aperture or entrance pupil. Example: f/8 means that the lens has a focal length eight times the diameter of the entrance pupil. Syn. f/stop; f-value; focal ratio; lens speed. See relative aperture.
Table F1 Sequence of f numbers used in photography with the corresponding relative image brightness and exposure time to maintain constant film exposure. The relative image brightness is equal to the square of the f number fraction
f numberfocal length/pupil exact
f number
diameterrelative image brightnessrelative exposure time
f/0.50.5f/0.5001/0.250.12
f/0.70.7f/0.7071/0.50.25
f/11f/1.0001/10.5
f/1.41.4f/1.4141/21
f/22f/2.0001/42
f/2.82.8f/2.8281/84
f/44f/4.0001/168
f/5.65.6f/5.6571/3216
f/88f/8.0001/6432
f/1111f/11.3141/12864
f/1616f/16.0001/256128
f/2222f/22.6271/512256
f/3232f/32.0001/1024512
References in periodicals archive ?
Table-6 shows that the calculated F-value is more than the table value and hence, it is inferred that there is highly significant difference among respondents regarding the empowerment benefits with different levels of payment of the loans.
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Looking at the F-value of Table 2, it should be noted that the most significant parameter was aging cycle followed by the type of substrate and the interaction between the substrate and aging cycle.