I shot some fireworks tonight. I was setup across the bay (Spanish Banks) with my tripod rooted in the sand, bag suspended from underneath for added stability, 70-300mm f4-5.6 IS USM lens, and my RC1 remote triggering the shutter on my 7D. I was using shutter speeds of either 2.5 or 3.2 seconds (tried some of each) and f-stops of 5.6 and 8. The exposure worked fine and one in five images turned out nice and sharp like the following... However, 4 in 5 pictures suffered from some some kind of movement and came out blurry (note the buildings below) which I have to assume is shake from the mirror or some artifact of leaving Image Stabilization on (didn't even think of that until I got home)... What's your thoughts as to what's causing this blur? Should I lock up the mirror? Should I keep IS off when on the tripod? Any other thoughts?