Ok, I just purchased the 70-200mm L lens, great lens. Freaken chrystal clear images. It burn holes in my kit lens. Wow, this lens is amazing. My question is what is the distance range switch. My thought is it's just for fast focusing on images at a set distance. My camera is a Canon BTW. But it has 1.4mm and 2.5m switch. What's it for? Is it just used to focus quickly on a subject? Thanks again, Grav.