Stereoscopic vision

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Stereoscopic Vision is the ability to see in depth. Stereoscopic vision is most important for predator animals who catch their prey, but has secondary importance for animals who are chased. Both eyes seeing the same scene reduces the field of sight and also allows other animals to sneak up undetected and attack. Prey animals prefer a panorama view of the wild, where their eyes are placed on each side of the head for more to see, allowing nearly a 360 degree field of view.

Humans, according to some theories, are claimed to be modified tree apes. Tree apes swing from branch to branch and failure to instantly judge the world in 3D could lead to a bad fall. Just like a camera, light rays cross over in the lens so the picture on the retinas are upside down as well as front to back. The brain has no trouble with that and just interprets the information.

Our eyes are separated by about 65 mm so the world seen by each retina is rather different. The difference is great for objects nearby, but not helpful for distant things, like trees, and other landscapes. Stereoscopic vision stops at about 200 meters, because the difference between the two retinal images is then unreadable. The 200 meter limit can be measured, but it is not a practical concept. In standard stereoscopic photography useful 3D stops way short of 200 meters, but it can be extended far beyond unaided human ability by using hyper-stereoscopic photography.

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