In human vision, convergence is the ability of our eyes to divert their optical axes so they meet at the object we are looking at. The convergence ‘near point’ is the closest point which is still possible to perceive one image. This can be easily found by moving your finger towards your nose; when you start to see it as two fingers, that’s the near point. Our eyes can easily converge inward but have much less ability to diverge outward; it is something we don’t do normally except when looking at 3D images that have positive parallax (requiring eye to diverge, point outwards) wider than the distance between our eyes (interocular).
In cameras, convergence is ‘toeing’ of the cameras (to simulate the eyes converging) to focus on a depth point in a scene, either in front of, behind or at the point of interest. The ‘convergence point’ is where the axes of toed in cameras align on the Z-axis. Convergence can be adjusted in post production by horizontal movement. Note that sometimes the term ‘vergence’ is used to describe both convergence and divergence.
Convergence pullers are camera-crew members on a stereoscopic shoot responsible for setting up and shifting the convergence during a shot.
See also: Parallax