Hi all, I've got a basic question. Even though I've been using an SLR for a number of months now, I've never learned about the distance (feet and meter) markings on a lens. What are these markings for and when would I use them (I assume they're for focal distance, but I can't figure out how they would be applied). Also, I hear the term "focus at infinity" a lot -- can anyone explain exactly what this means and when one should focus at infinity? Thanks.