F- Stop

Article:   http://www.canadiannaturephotographer.com/fstop.html

When using F-stop, the diameter opening of the lens determines how much light enters the lens, and how much in the picture is focused. If the lens aperture (opening of lens) is wide, the number of the f-stop is smaller, and vice-versa.  A large F-stop number will result in a small lens aperture and more things will be in focus. The f-stop number determines about how many feet the lens will focus on. For example, the f-stop is at 1.3, the lens will focus on whatever is about 1 foot away and everything behind it will be blurred out. If the f-stop is at 10, the depth of field will become greater meaning the lens will focus on more things than when the f-stop was 1.3. With a smaller f-stop, the shutter is faster. This means the picture is taken at a faster speed because the shutter opens faster.