From the comment here http://vimeo.com/12828140 http://vimeo.com/12828140 it looks as if this guy isn't even using a beam splitter, just two wide angle lenses.

From the comment here http://vimeo.com/12828140 http://vimeo.com/12828140 it looks as if this guy isn't even using a beam splitter, just two wide angle lenses. I think that most of the magic in this technique is in the luma keys. (duh...)