I did some searching and I can't find what I'm looking for. Basically, I have a Sigma 70-200mm f/2.8 lens and the pictures are not coming out as crisp as I'd expect for a $1300 lens. I am taking pictures of football games under the lights. I'm not getting blur like I did with my cheaper lens, and the pictures just aren't crisp. Any settings on the camera I can change? Any other tips?