Blurring the background is a very commonly used photography technique to emphasize the subject and to avoid busy or distracting background. In photography term, you want to have a shallow depth of field (DOF) that only allows a narrow range of sharp focus. Here are a few very easy tips:
Focusing at a closer distance will reduce the DOF. The focal length of your lens may limit how close you can get. For example, it is preferred not to get too close to for a portrait photo with a wide angle lens to avoid odd-look distortions.
Use lens with longer focal length
At the same camera to subject distance, lens with longer focal length will produce shallower depth of field. An added benefit of long lens is that it also has a narrow angle of view, therefore making it easy to avoid background distraction, such as a power pole, trash can, or hash reflection spot, etc.
Open up the lens aperture
The wider the aperture (the small the f-stop number), the shallower depth of field is. Professional grade lenses can typically open up to f/2.8, or even f/1.4. Some budget lenses may not have such large aperture so you just have to open as wide as possible if the DOF is not shallow enough. In many practical cases, you do not want to use maximum aperture for a couple of reasons: first, the DOF may be too shallow to contain all parts of the subject that need to be sharp; second, the image quality may be degraded due to distortion and chromatic abbreviation. You may want to know more about your lens to make a decision on whether the image quality is good enough.
Use the depth of field preview button
Many digital single lens reflex (DSLR) cameras have a DOF preview button. In typical photo-taking process, the camera sets the aperture wide-open to give user a bright viewfinder. When the shutter release is pressed, the camera will set the aperture to the intended f-value. If the intended aperature is already the maximum aperture of your lens, pressing the DOF preview button has no effect, although you may still hear a click.
The above are the basic tips of taking photos with less distracting background. Please comment below or drop me an email at picmax at gmail dot com. The excellent photo in this post was taken using a 90mm lens at f/3.8.