I have a Sigma Zoom 100-300mm f4.5 6.7 lens and have noticed that the photos seem fuzzy / blurry. I notice it mostly at 300mm as that is the zoom that I usually use it at. It is not camera motion as it happens even on a tripod at 1/1200. I was wondering why it is fuzzy, is it quality of the lens? Is there anything I could do to fix this problem?