Focus?

Hey, I just got a quick question for an animation experts out there.


I'm seeing a focus and blur effect more and more in flash. Like the background will be blurry (as if shot by a camera) and the foreground or subject will be in focus, then they switch. Anyone know how to do that?

I'm starting work on a big new animation and If i could figure that out it would add a whole new level to the visuals. Please someone, help me out. Thanks