Should stereo 3D cameras be kept parallel or angled inward at the subject?
Asked 7/14/2013
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When shooting stereo 3D photos or video with two cameras, should the cameras stay fixed parallel to each other, or should they be rotated inward so their optical axes converge on the subject, similar to how our eyes turn inward when focusing on something close? I often see behind-the-scenes 3D rigs with both cameras kept in a fixed parallel setup and want to understand whether that is the correct approach or just a technical compromise.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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Keep the cameras parallel and coplanar.
Unlike the human eye, most cameras have a flat, not spherical, sensor. That means that if you point the cameras in different directions, you will get a different perspective view from each. If you look at a rectangular object, for instance, one "eye" will see the left side of the object taller than the right, and the other "eye" will see the opposite. That effect will be there to an extent with parallel cameras, but it's more or less what your eyes will see in normal operation (because they are spatially separated). Aiming the cameras to converge will exaggerate the effect, making it more difficult for the brain to align the images.
Originally by user2719. Source · Licensed CC BY-SA 4.0
user2719
13y ago
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For stereo 3D capture, the usual guidance is to keep the two cameras parallel and coplanar rather than toeing them inward.
The main reason is that cameras use flat sensors, unlike human vision. If you angle the cameras toward each other, each camera records a different perspective distortion. For example, a rectangular subject may appear skewed differently in each view: one side looks taller in one camera, and the opposite side looks taller in the other. That mismatch makes it harder for the brain to fuse the pair comfortably into a 3D image.
With parallel cameras, you still get the left/right viewpoint difference needed for stereo, but without exaggerating those perspective conflicts. So the fixed parallel rig you see is generally the preferred setup, not just a technical limitation.
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