About BS oplev, its optical axis will be vertical, so it is relatively difficult for adults; maybe easier for japanese elementary school students.

One notice on this system is the angle of the axis is 37 degrees. Newport is selling adapters for 45 degrees for their mirror holders, which has a range of +/-7degrees, and that means even the combination of the adapter and the mirror holder cannot cover 37 degrees!!!!

Hmm, well, maybe I'll design a stuff...