A term used to describe the aperture, or diaphragm opening of a lens. F-stops are defined numerically: f/1.4, f/5.6, f/22, etc. Larger, or wider apertures, allow more light to enter the lens, which calls for faster shutter speeds. “Faster” (wider) apertures also allow for selective focus (narrow depth of field), while slower (smaller) apertures allow for greater depth of field. Wider apertures are preferable for portraits, while smaller apertures are preferable for landscapes.
Sequence of f-stops are multiples of the square root of 2 (1.414…): 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, etc. Even though these numbers are rather cryptic, just remember that each step is double the amount of light. Know that and it’s half the battle.
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