OK, I'm stuck. It appears that a section of the printed documentation is missing, it says "see below for instructions" but there doesn't seem to be any. It mentions removing an infrared filter first - I don't see where it is. The inner lens assembly sticks out just far enough to block the slot where the diopter lens should go, leading me to believe that the IR filter is behind (internal) to the lens assembly. Is there a diagram or tutorial that shows how these are supposed to be installed?