You may have noticed that iOS 5.1 changed the behavior of the lock screen camera compared to it’s predecessor, this has caused some confusion as to how it works compared to iOS 5. You’ll notice that if you tap on the camera icon now it just causes the screen to bounce. No, the bouncing screen doesn’t mean the camera isn’t working anymore, it’s aim is to indicate how it works.
You now swipe up to activate the lock screen camera in iOS 5.1. Likewise, you can swipe down to deactivate the camera and return back to the lock screen.