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
Diaphragm (optics)
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In optics, a diaphragm is a thin opaque structure with an opening at its center. The role of the diaphragm is to stop the passage of light, except for the light passing through the aperture. Thus it i
Pentacon 2.8/135 lens with 15-blade iris
Aperture mechanism of Canon 50mm f/1.8 II lens, with five blades
In the human eye, the iris (light brown) acts as the diaphragm and continuously constricts and dilates its aperture (the pupil)