First some background: Left/right eye separation

0
124

Depth in or out of the screen is created when the left eye and right eye views cause viewers’ eyes to cross at a point in front of or behind the screen.

Adult eyes are, on average, separated by about 2.5 inches (65mm).

Now think about looking at a ball on a screen when the right eye’s view of the ball is 2.5 inches to the left of the left eye’s view of the ball (negative parallax). When exposed to viewers with a proper projection system, each image will cause each eye to track the ball independently, crossing at one half, or 50%, of the way to the screen. (If you question this, sketch the scene looking downward to see its geometry.)

On the other hand, if the ball in the right eye’s view is 2.5 inches to the right of the ball in the left eye’s view (positive parallax), the axis of the eyes’ vision will be parallel. In this case the ball will appear to be at infinity — just like when you look into the distance.

Normal eyes do not ever diverge apart. Therefore, if you see positive parallax on the screen exceeding 2.5 inches, be aware that the scene will be creating an abnormal and difficult viewing experience, and one likely to cause discomfort.

Similarly, if the negative parallax exceeds 10 or more inches, the scene is presenting objects at or closer to you than 20% of the screen distance. That also may be very difficult to view for any extended length of time.