You can dramatically change the look of your photo by changing the aperture of the lens on your camera, which controls the depth of field. Depth of field is how much of your photo in front of and behind your subject is in focus. If foreground to background is all in focus, your depth of field is deep. If the foreground and background are out of focus, then you have shallow depth of field. Learning to control this function on your camera will help you to yield more professional-looking photos that let your subject pop off the image because it will be separated from the background. In the two example photos below, the one on the left shows shallow depth of field. The aperture was set to F/4.5 (a wide open aperture). The photo on the right shows deep depth of field and the aperture was set to F/16 (a small aperture).
The aperture is easy to set on your camera by setting your camera mode dial to A (on Nikon cameras) and Av (on Canon cameras). Then use the thumb wheel to move the aperture number to a smaller or a larger number. The smaller the number, the more blurry the background will be like the above left photo. The larger the number, the more in focus both subject and background will be, like the above right photo.
This technique is particularly useful when shooting portraits. You want your subject to stand out from the background, especially if there are distracting items behind the subject. You can choose how blurry or sharp the background will be by experimenting with different aperture settings. To practice, shoot the same subject twice at the two extremes like I did above. Do this several times with different subjects each time you have your camera out until you feel comfortable that you can easily pick the aperture to get the look you want. See more examples below and don’t forget to download the photo tips card for your gadget bag to help you in the field.