Stereo 3D Dolly Zoom

A dolly zoom in stereo 3D. As the camera rig moves closer to the head, the focal length (horizontal angle of view) becomes wider. The zero parallax plane is just in front of the base of the ears.
The ratio between the base separation of the right and left cameras and the distance from the middle of the base to the zero parallax plane is locked at 1/20. In other words, the cameras move closer together as they dolly closer to the head. You can see that the back wall does not change in depth, and the head shape changes very little.
If the base were set to remain constant during the dolly toward the head, the stereo depth would increase progressively.