Distance between stereo camera lenses in 3D production — controls depth perception and convergence. Too wide causes viewer strain; too narrow kills the effect.
The distance between the two lenses of a stereo 3D camera directly determines how spatial and natural the depth effect appears on screen. When shooting with two synchronized cameras—or with specialized rigs like the Pace or James Cameron's Fusion—you adjust this distance to the millimeter. It essentially functions like the interpupillary distance in humans, only you can manipulate it.
In practice, this means: An interaxial distance of approximately 65 mm corresponds to the average human interpupillary distance and creates a comfortable, natural stereo effect. If you go below this—around 40–50 mm—the depth appears flat and artificial, especially in close-ups. This can be intentional, for example, for a compressed lens effect or for scenes with reduced spatial tension. If you reverse this and increase the distance to 100 mm or more, you intensify the depth exaggeration—the image gains an almost exaggerated spatiality, which quickly leads to headaches and visual strain for the viewer. The eye cannot comfortably maintain extreme convergence.
The interaxial distance works closely with the convergence point—the point where the two lines of sight meet. The larger the distance, the more one camera must be rotated inward to focus on the same point. Some DPs adjust only one of the two lenses, while others work with digital convergence in post-production. This is a matter of taste and depends on your equipment.
On set, this is not just any technical detail—it is your creative control over perception. For close-ups, I often consciously reduce it to stay closer to the actor's eye. For landscapes, I increase it to truly feel the distance. You need to test and calibrate, ideally with on-site monitors where the stereo output is already visible. Much can still be corrected in post-production, but shooting blind on set means unnecessary rework and risk.