These images demonstrate how you can manipulate the relationship between the background and foreground in your image. To create this effect focus on your main picture element in the foreground. Then move further back away from the object, and zoom your lens to maintain the same size of the picture object. As you move further away the background effect will become more dramatic as shown in the frustration. Here is a tutorial if you would like to watch it on this subject.
http://gallery.me.com/d.higgins/100464