Aperture . Origin: late Middle English, from Latin apertura, from apert- 'opened,' from aperire 'to open.'
In a camera, the aperture refers to the lens diaphragm, or how wide the opening is that allows light to goes through. This determines just how much light hits the piece of film or digital sensor.
The aperture is one of the fundamental tools in photography. When used in connection with shutter speeds, the aperture allows tremendous creative control.
By adjusting the aperture, you determine the range of distance that will be sharp and in focus, known as the photograph's depth of field.
Most lenses will have an aperture ring that you adjust manually or electronically to open up or close down the diaphragm. If you look at your lens, you should see a series of numbers called F stops. A typical lens might be engraved with the following : 2, 2.8, 4, 5.6, 8, 11, 16 and 22. The difference between each f stop varies by a factor of two, with f2 letting in twice as much light as f2.8, or conversely, f16 letting in half as much light as f11.
Practically speaking, using a smaller aperture (such as f16) will give you more depth of field, useful if you want to take photographs with everything in focus and sharp.
Alternatively, a larger aperture such as f1.4 will have a very shallow depth of field, rendering everything in front of and behind the plane of focus to be rendered out of focus, the degree determined by the aperture.
Portraits benefit from a relatively shallow depth of field, so that distracting backgrounds are kept to a minimum. The aperture you use will depend on the type of photograph you want to create with your camera.
A useful exercise is to experiment with different subjects and apertures to find a look that you like, so that when the time comes for that important once-in-a-lifetime photo, you'll be ready to take advantage of everything your camera offers.
See the photo gallery for how pictures change depending on their depth of field.