Hello, I was curious as to how the Auto-focus actually functions. I'm mostly interested in how the AF-C functions. For the sake of simplicity, lets say that I only have the center square focus point active, if it matters, its on a D7000. How does the auto-focus continuously keep that in focus as it moves? Does it "memorize" the colours in that set of pixels? What happens if the target moves out of the "active focus square"? What happens if something moves between the target and the camera?