So far, everything I have had been passed down to me. Anywhoo, what do I need to know about buying new lenses? I'm pretty sure "IS" stands for Image Stabilzers But what about that USM stuff? Can someone explain to me what I am looking for and what I shuold be aiming at? Edit (thanks to usayit): My budget is very low, I'm down for about 200-300 per lens right now. I'm shooting with a Pentax IST DL which requires a K-Mount lens. I was thinking of the Sigma 24-124, not quite sure the specifics on it, but some people weren't a big fan ofr that lens.