A stereoscopic viewing apparatus for viewing side-by-side complimentary stereoscopic image pairs of various sizes to produce a three-dimensional effect, the stereoscopic viewing apparatus comprising a pair of left and right spaced-apart ocular windows and variable septa....http://www.google.fr/patents/US6487013?utm_source=gb-gplus-shareBrevet US6487013 - Folding prism stereoscope
