The aperture is an opening in the lens that allows light to strike the image sensor to create an image. The wider the opening, the more light is allowed to affect the exposure. Every aperture is designated by an f/number. The smaller the f/number (e.g., f/2.8), the larger the opening (this allows more light to enter the camera). The bigger the f/number (e.g., f/22), the smaller the opening (this allows less light to enter the camera).
The aperture also offers control over blur. When you use a wide-open aperture (e.g., f/2.8), you get a shallow depth of field. In other words, very little of the scene in front of and behind your focus point will appear in sharp focus. When you choose a small aperture (e.g., f/22), the depth of field is much wider. In other words, the focus falls off much more slowly. You can see a wide band of focus in front of and behind the subject.
Depth of field is important to the creative photographer. Once the artist with a camera decides on his aperture setting, he does not waiver. It remains locked in. The consequences of a change of aperture should be intolerable.
Larger apertures (smaller f/numbers) offer less depth of field.
Smaller apertures (larger f/numbers) offer greater depth of field.
Depth of field is controlled by the aperture, the focal length, and the focus distance. Larger apertures, longer focal lengths, and shorter focus distances all give you less depth of field. This means that the closer you are to the subject, the more you zoom in, and the bigger the aperture, the more you can blur the foreground and background. Conversely, the farther away you are from the subject you’re focusing on, the less you zoom in, and the smaller the aperture you choose, the more things will be in focus throughout your image. With all three factors working together, an artist cannot fail to get the look he is after.
