I've been working on a camera system similar to what you're describing here, and I've finally landed on a solution that works for me.
I made a simplified version as an example Capx. It's a little complex, but I tried to annotate the example so it would at least make some sense. Let me know if it helps, or if you have any questions.
Metroid-ish Camera System -- Example CapXwhiteheat2012-09-10 19:25:18
Hey, thank you so much, this is brilliant, but Now I am wondering if you know how to do the room transition in metroid where you walk into the door, and then everything goes black except for the door, and then it slides across the screen?