Convergence & Divergence
Binocular Vision and Parallax are the primary visual tools animals use to perceive depth at close range.
The wider an animal's eyes are apart (its interocular distance) the deeper its binocular depth
perception or "depth range. "
At greater distances we start to use monocular depth cues like perspective, relative size, occlusion,
shadows and relation to horizon to perceive how far away objects are from us.
Of course it would be difficult to look at double images all day so instead our eyes naturally angle in
towards the object of interest to make it a single image. This is called convergence.
Here's an example of how your eyes use convergence in the real world. Hold a pen about one foot in
front of your face and look directly at it. You will feel your eyes both angle towards the pen in order
to converge on it, creating a single image of the pen. What you may not immediately perceive is that
everything behind the pen appears as a double image (diverged.) Now look at the background
behind the pen and your pen will suddenly appear as two pens because your eyes are no longer
converged on it. This "double-image" is retinal disparity at work and it is helping your brain determine
which object is in front of the other.
What never happens to your eyes in the natural world is divergence, which would mean that your
eyes would angle outward. This is because the furthest point you could possible attempt to look at is
at in nity and even in nity would only require that your eyes be angled perfectly parallel to each
other. This is why stereographers should avoid background parallax values in their scene that may
require the eyes to diverge when viewed. This is easy to keep in check through some simple math
but we will cover that a little later.
Converged Eyes
XF300/305 Whitepaper
Tim Dashwood
Diverged Eyes
Stereoscopic 3D
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