I'm getting a GRD IV soon and am wondering what the diff between snap vs zone vs infinity vs hyperfocal. I've tried to read up on it via googling but I still can't wrap my head around it. It know it has something to do with pre-focusing so it takes a pic instantly when object comes into the frame and when you click the shutter. Are these the same thing but different naming? Can all cameras do this? Does AF need to be turned off?