Well, in this case, half a sphere coated in reflective material with a hole at the top, suspended above the camera with a mirror on top of it. But it makes pictures like this (mounted on the plane):
Now it needs some processing before it's something you can look at without getting a headache. So after relearning some of high school's math (if you ever wondered why do you need to know something in Cartesian and Polar coordinate systems, this is why) this is the result:
Hm, needs some more work.