OK, double post time for me. Apparently the RM72 isn't totally opaque, but it is dark enough that one couldn't exactly see through it to focus, even at f/1.2. So let's tweak the question here - what is the darkest IR filter that one can actually see through to focus? I'm beginning to think that one can't really do handheld IR with the Maco stuff - if it needs something in the range of the opaque and near-opaque filters for good effect, then one can't really just stand there shooting in a vaguely normal manner. Maybe I'll stick to HIE after all...