F Stop

The f-stop is the aperture opening of a camera lens, which allows light to come in. The f-stop is the focal length of the lens divided by the diameter of its opening. Each consecutive f-stop halves the opening of the previous. For example, an 80mm lens with its f-stop set to f/8 means that the optics inside the lens create a diameter equivalent to 10mm. Changing the f-stop to f/16 creates a diameter of 5mm.