Here's
an article that discusses in detail some of the theory and methods behind cameras in 2D games. I'd seen it quite a while ago, perhaps when it was first published last May, but I recently rediscovered it and thought it was worth sharing. What surprised me most about it is that complex camera systems in games mostly seem to come down to just a few simple (but clever) tricks, but when combined it results in quite elegant behavior.
A few years ago mouser posted about
a video analyzing the camera behavior in Super Mario World. While hearing it explained while seeing the game was interesting, I found this newer article to be much more useful in seeing how things work because the areas of interest are visualized for us, like so:
It's a fairly long article, but it goes into some really useful detail analyzing how many popular/classic games have designed their camera system to allow the player to see important information in the game.
Highly recommended.
http://gamasutra.com...in_SideScrollers.php 
