Wow! Impressive.
And I only see one person in the group with her eyes closed: the gal at the lower left, front row. How do you get them to keep their eyes open? I shoot a large chorus every year when I'm down in Florida. Of course I shoot a whole series of exposures because if I shoot one or two I'll almost always have somebody with closed eyes. But I also start out by telling them that the most difficult part of the shoot is to make sure everybody's eyes are open. I also tell them that if they can't see the camera the camera can't see them. Then I tell them that I'm going to say "eyes open" just before I hit the shutter release. Works like a charm. Oh, and they're up on risers so I don't need that beautiful 15 foot tripod.