When looking at a painting, the television or a photo we perceive the depth only through secondary stereopsis elements (look at the previous section   Stereoscopic vision); using only one view (eye), we don't therefore leverage the more precious possibilities offered through our two eyes in the primary stereopsis process.

Sir Charles Wheatstone, in the very same years of the discovery of photography (around 1830), invented a device which could exceed this limitation of the monocular representation and called it Stereoscope.

Several versions of these devices can be found even nowadays in antique-trade shows.

The idea was surely very simple: taking two photos related to what our two eyes record and then find a way to make the left eye sees only the left image and the right eye only the right image; in this way, our "cheated" brain could fuse them together restoring the depth dimension.

In times in which television was not already invented and it was not easy to travel around the world, families of the end of the 1800 and beginning of the 1900 were meeting and with these stereo devices were dreaming about Pyramids, the Roman Forum or the Yosemite Falls.

The apex of popularity for the stereoscopic images was reached during the half of the '50s of the last century when 100 million of View-Master viewers and one billion reels were sold .

Stereoscopy is not just Art but has been exploited also for scientific purposes.

Can you imagine which sophisticated devices we use to record landscapes when exploring Mars, for instance ? Two little displaced, horizontally mounted and with parallel lenses axes photo cameras. The lessons from Sir Charles Wheatstone are tremendously valid even nowadays.

If you want to have a look at the Mars Anaglyphs just go to our    Gallery or to other sites like    JPL-NASA.