I am researching buying a DS-2CD2542FWD-IS 4MP 4MM camera and mounting it on my front porch about head height over the front door bell. Most of the time it will be looking at the driveway, the street, and the entrance to an alley beside my home. However when someone comes to the door they will be much closer and I'm worried that if I focus on the street that a person at the door will be too out of focus to see clearly and vice versa. Anyone have any experience with this camera? Would the 2.8 or 6.0 MM lens suit me better for this?