Try double vision: Look at a near object. Press one of your eyes slightly. You'll see two separate images."Binocular" is to see with both eyes simultaneously.
"Stereoscopic" is to see things as 3-dimensional.
Each eye has a fixed visual angle. In our eye, the angle is 104°. Since our two eyes are placed close together, overlapping of visual angles results. This allows more accurate judgement of distance of the object in front of us.
To see 3D, when our 2 eyes focus on one object, slightly different images from both eyes are sent to the brain, where the impulses will be fused to compose a single image. If our extrinsic eye muscles cannot function well or when we are under the influence of alcohol, double vision, i.e. diplopia would occur.
Try double vision: Look at a near object. Press one of your eyes slightly. You'll see two separate images.
Good binocular & stereoscopic vision is important for animals who are predators, e.g. hawks and lions. They have to accurately judge the distance to catch prey. Their eyes are set in front.
Other animals, e.g. a rabbit (a common prey), has an eye on each of the two sides of its head. It has a wide overall visual field, which is good for detecting movements. But little overlapping of visual field results in poor stereoscopic vision.
The animals with eyes on the sides of their head rely on 1)the relative size of an object, 2)the shadow it creates, 3)the movement of it relative to distant non-moving objects, to judge distance.
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