Aperture refers to the amount of light that the camera's "eye" lets in to illuminate the film or sensor.
The word photography means writing with light. There is no other part of the camera that makes such a meaning more definitive than the aperture. The aperture is the camera's light collector, the aperture controls how much light gets in and how much light stays out. Understanding the aperture is a crucial first step to controlling and eventually mastering initial camera technique in photography.
Collection of Light
The aperture is to the camera as the iris is to the eye. The aperture size refers to how much light is let into the camera to be reflected on the sensor or film. As with the human eye, when the iris contracts itself, the pupil becomes smaller and the eye takes in less light. When the iris widens in darker situations, the pupil becomes larger and takes in more light. The same effect happens with the aperture; the larger (lower) the aperture value lets in more light than a small (higher) aperture value. The lens opening is the pupil; the smaller the opening, the less light let in. Therefore, controlling the aperture setting means controlling the light.
F-Stops
Aperture sizing can be confusing for those just beginning with single-lens reflex (SLR) cameras, whether film or digital (DSLR). Aperture is measured in terms of f-stops, ranging from f/1.2 to f/22. The smaller the f-stop number, the larger the aperture value---small is large. The general range of usable aperture values are f/1.8, f/2.8, f/4, f/5.6, f/8, f/11 and f/16.
Maximum Aperture
A larger aperture (smaller number) has a greater advantage over larger apertures as it allows for the use of faster shutter speeds (amount of time light is let in) that enable the photographer to capture fast-moving objects. The more light that reaches the sensor of the camera prior to shutter movement means less time open to exposure. Blur happens in a photograph when the speed of the object is too fast for the speed of the shutter to capture. Sport and movement are generally shot with low apertures to allow for fast shutter speeds to catch the motion sharply. Large apertures also allow for a more shallow depth of field than smaller ones do, that is, the subject is in focus and the background is blurred.
Minimum Aperture
The advantages of larger apertures do not imply that small apertures are useless. A smaller aperture allows for the use of a slow shutter speed in extreme light, and enables motion effect in the daylight. Minimum aperture also allows for greater depth of field, that is, a small aperture will focus more of the image regardless of the depth.
Set It
On most SLR film cameras, aperture is set using the ring around the lens that is closest to the base. The aperture settings will be listed by f-stops. On some DSLR cameras, changing the aperture is usually (not always) achieved by a small scrolling button to the front-right side of the camera. Scrolling the aperture button to the left increases the size (smaller number) and scrolling to the left decreases the aperture size.
