When you're ready to move beyond the automatic controls of your camera, the aperture setting might just become your best friend. This manual exposure feature allows you to blur unattractive backgrounds, sharply focus a wide landscape shot and even brighten a dim scene. By adjusting the aperture setting on your single-lens reflex camera or fully loaded compact camera, you can partially control the amount of light entering the camera and the overall look of your photographs.
Aperture and shutter speed work together to expose an image on your camera's digital sensor or piece of film. The shutter speed determines how long light flows into the camera, while the aperture setting controls the size of the aperture ring opening in the camera lens where light flows through. Aperture settings are referred to as f-stops, or focal ratios. The larger the f-stop number, the smaller the opening, and less light is used to expose the photograph. F-stop numbers are derived from dividing the focal length of the camera lens by the diameter of the aperture ring in the camera lens. An aperture of f/8 is wider and allows more light into the camera than an aperture of f/16.
Depth of Field
The aperture setting -- noted by an A or AV on a camera's command dial or settings menu -- in part determines how much depth of field you notice in a picture. The more light that comes into the camera, the more shallow your depth of field. If you're looking for a shallow depth of field or to brighten a scene, pair a telephoto lens -- with at least a focal length of 105mm -- with an aperture setting of f/2.8 or f/4. By using a long focal length and allowing ample light into the camera, you can blur the foreground or background, making the other stand out. Think of a flower picture where the flower appears tack sharp and the green grass beyond the flower appears smooth and green with no detail.
If you want your entire scene tack sharp from foreground to background, use a wide angle lens. Set the aperture for a deep depth of field with a setting such as f/16. This will close down the aperture ring in the lens, allowing less light to enter the camera, which increases depth of field and detail.
Portrait photographers, sports shooters and others who seek to focus on one individual at a time often use the aperture setting to isolate their subject against the background. If you want to see a football player making a pass, but are bothered by the busy background of cheering fans, set your aperture to the lowest number possible on your camera, such as f/2.8. This will blur everything beyond your focusing point, which in this case is the football player.
Landscape and scientific photographers want to capture as much detail in their images as possible. They often use aperture settings to decrease light flowing into the camera so fine details are recorded and not blurred or washed out. If you want a detailed picture of a mountain scene, set your camera aperture to f/22 and place the camera on a tripod to steady the camera because the exposure may require a long shutter speed. By setting an aperture of f/22 with such a deep depth of field, the grass in the foreground should be as sharp as the distant mountain peaks in the photograph.
Reducing Unattractive Backgrounds
The aperture setting also works to reduce bothersome backgrounds. If you are trying to take a picture of a family picnic in a public park, but an old rusty car just parked behind the group, use the aperture setting to focus on the group, but blur the details of the distant car. For a group you need to increase your depth of field so people in both the front and back rows appear sharp. Experiment with settings ranging from f/4 to f/8 for a subtle transition between a sharply focused foreground and blurred background.