Abstract: A system for adjusting the relative position of the optical unity axes used in viewing images of associated couples. In order to permit a satisfactory cerebral fusion when two images present a displacement in their positioning, a viewer is equipped within the optical block having the cylindrical and lateral surfaces and co-operating with surfaces of complementary forms and of the baseplate. Ocular circles define the position of the observer's eyes. The invention is particularly useful for projection onto a screen of pairs of stereoscopic images.