[hazeii]

I've been out of SFX for decades so can't speak for current practice; anything really black (classically velvet/black flock) is (was?) useful for hiding all sorts of things from the camera. So I'm just guessing here, but because cameras (more specifically the sensors) are much more limited than the human eye in terms of the range of brightness they can handle it's probably more useful in scientific/direct view applications.