The bane of concert photographers is the microphone stand. That’s for two reasons:
First, if the singer is doing his thing, the mic is likely blocking his face from your shot. That makes for useless pictures.
Second, every now and then, the autofocus grabs the mic and not the performer. I haven’t run the numbers in a DOF calculator yet, but the depth of field at f/5.6 from 80 feet away is surprisingly shallow.
Why didn’t I use manual focus, since I was using manual exposure? I’m not that good at manual focus, and I was taking pictures of people across a stage, probably 20 feet apart. Manually focusing every shot like that would waste a lot of time.
Funny story: I didn’t pay too much attention to the mic stand just to Steve Martin’s left (my right) as I was shooting. It wasn’t until I got home and started looking at the pictures before I saw what it was: an iPad! I’m not 100% sure what it was displaying for him, but I can see him glancing at it in some of my pictures. The future is here, isn’t it?