I tried using my pan 12-35 2.8 on Aurora display a few nights ago- looking at the results I wonder if I'm getting the focus quite right? I wanted the foreground trees to be sharp, so I had pre focused on them. But in others' Aurora pics I have seen, the lights appear far better defined. Especially in the last pic, in a tighter shot. The lights seemed to be moving a lot also, so maybe this is the reason? Is there an optimum exposure duration to "freeze" the shimmering aspect of Aurora? These frames were at 2.8, between 6 and 8 seconds, ISO 800 - 1600.