Helmholtz telestereoscope

telestereoscope, Helmholtz 

Instrument designed to produce an exaggerated perception of depth by optically increasing the length of the base line of the viewer, using a system of mirrors or prisms (Fig. T2).
Fig. T2 Optical principle of a telestereoscopeenlarge picture
Fig. T2 Optical principle of a telestereoscope
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann