Originally Posted by EventServices
No, the only way to blur the background with motion is to pan with the subject AT THE SAME SPEED. That keeps the film/subject relationship constant.
The trick is use a slightly slower shutter speed and to start your move BEFORE you pull the trigger.
Practice with cars on the road in front of your house.
Aperature, as it relates to focus, controls depth of field.
This description is spot on. The idea of using aperature (which varies the size of the opening in the shutter, not the time it is open) determines how much of the image will be in focus even if everything is sitting still. A good example in his slideshow of how to use depth of field to blur out unwanted background clutter is:
Notice how the crowd in the background is blurry, so they don't become too much of a distraction from the focal point of the image.