Two-Toe, Revisited

< Previous | Contents | Manuals Home | Boris FX | Next >

‌Two-Toe, Revisited

The camera parameters, as described above, describe the situation for “single- toed” camera rigs, where only one camera (the secondary) rotates for vergence. The situation is a little more complex for two-toe rigs, where both cameras toe inwards for vergence. These modes are “Center-Left” and “Center-Right” in the Stereo Geometry panel’s dominance selection.

The dominant camera never moves during two-toed vergence, yet we still achieve the effect of both camera tilting in evenly. How is that possible?

Consider a vergence angle of 90 degrees. With a one-toe rig, the secondary camera has turned 90 degrees in place without moving, and is now looking directly at the primary camera.

With a two-toe rig at a vergence of 90 degrees, the secondary has turned 90 degrees so it is looking at right angles to the look direction of the dominant camera.

But, and this is the key thing, at the same time the secondary camera has swung forward to what would otherwise be Direction=45 degrees, even though the Direction is still at zero. As a result, the secondary camera has tilted in 45 degrees from the nominal look direction, and the dominant camera is also 45 degrees from the nominal look direction—which is the perpendicular to the line between the two cameras.

The thing to keep in mind is that the line between the two cameras (nodal points) forms the baseline; the nominal overall ‘rig’ look direction is 90 degrees from that.

SynthEyes changes the baseline in centered mode to maintain the proper matching vergence for the two cameras; it does that by changing the definition of where the zero Direction is. The Direction value is offset by one-half the vergence in centered mode.

If you put the stereo pair into one of the Centered modes and use Live mode, you’ll see the camera swinging forward and backward in response to changes in the vergence. Once you understand it, it should make sense. If it seems a bit more complex and demanding than single-toe rigs… you’re right!

< Previous | Contents | Manuals Home | Boris FX | Next >