F number, Aperture, Shutter speed
Aperture is, put simply, a hole, and in terms of photography, a hole in the lens through which light travels when the shutter button is depressed.
The size of an aperture is referred to as an f number. F numbers are referred to as f-stop or f/number. A principle that really confuses new photographers is that a larger aperture (larger hole, more light, ) is actually given a small f/number, so even though f/2.2 is a larger number than f/1.0, the latter has a larger hole. A set amount of light is needed to take an image, and as moving from one f stop to the next doubles or halves the size of the opening, so the time needed to take an image is doubled, or halved. When moving to a lower number, shutter speed time doubles. And when moving to a higher number, it halves.
Blink quickly. You have very little time to gather in your surroundings, and so you see a much shallower depth of field. Open your eyes, take in your surroundings, then close them again. This time, your depth of field was much deeper, because your eyes had more time to see things around them. This is just the same digital with cameras. While you may get a much faster shot with a low f/number, (this is especially good for action photography, because it freezes the subject in motion, all you see is the subject, with a blurred background, while a higher f/number gives you a motion blurred subject, and an in focus background, so higher f/numbers are more suitable for landscapes and still life.
An accurate knowledge of aperture is essential when using manual or aperture priority mode, and also helps to greatly improve your photography. These pictures where taken with a compact camera, and this has a small sensor, meaning that its depth of field is deeper than a DSLR.
make quite a good example.
F/2.0 here you can clearly see how shallow the
DOF is, only the first eraser is really in focus.
F/5.6 here you can see how most of the
eradicators are in focus.
has the deepest DOF.