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Definition: The f-stop, short for focal-stop, is the numerical measurement of the aperture settings in a digital camera lens. A higher f-stop setting means less light is allowed through the adjustable opening inside the lens to strike the image sensor.

To determine the f-stop, divide the focal length of the lens by the diameter of the opening. For example, if you have a 50mm lens with a diameter of 6.25mm, the f-stop is f8. Each larger f-stop halves the diameter, meaning f16 would be a 3.125mm diameter.

Also Known As: focal-stop
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