The manual for my 60mm f/2.8 lens doesn't match my lens. My lens has an adjustment ring near the base with numbers (32 22 16 11...2.8). 32 is red and that's where it's locked in. What is this ring for? Is it for calibrating? Do I need to get some kind of calibration kit? Thanks. edit: duh, nevermind. it's the manual f-stop ring.