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Symbol: F, f / Base data: Numerical aperture.
Unit that indicates the brightness of optical systems such as the lens of a camera or telescope. Ratio of the system's focal length to the diameter of the entrance pupil.
Value indicating the adjustment of an “aperture”
Photographic images are governed by “aperture” and “shutter speed”. An “f-number” is a unit that indicates the adjustment of the “aperture”. Try to remember it as follows: if the value is small, the background can be defocused, and when it is large, the background comes crisply into focus.
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