F-number
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An f-number is a measure of the light-gathering ability of an optical system such as a camera lens. It is defined as the ratio of the system's focal length to the diameter of the entrance pupil. The f
A Canon 7 mounted with a 50 mm lens capable of f/0.95
A 35 mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring. This lens has an aperture range of f/2 to f/22.
Comparison of f/32 (top-left half) and f/5 (bottom-right half)
Shallow focus with a wide open lens
Depth of field
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The depth of field is the distance between the nearest and the farthest objects that are in acceptably sharp focus in an image captured with a camera. See also the closely related depth of focus.
F-number
…diameter of the entrance pupil ("clear aperture"). The f-number is also known as the focal ratio, f-ratio, or f-stop, and it is key in determining the depth of field, diffraction, and exposure of a photograph. The f-number is dimensionless and is usually expressed using a lower-case hooked f with the format f/N…
A macro photograph showing the defocused effect of a shallow depth of field on a tilted page of text
This photo was taken with an aperture of f/22, creating a mostly in-focus background.
The same scene as above with an aperture of f/1.8. Notice how much blurrier the background appears in this photo.
Aperture = f/1.4. DOF = 0.8 cm