Practice : aligning the cameras

Cameras and lenses must be, obviously, exactly identical.

The perfect alignement, pixel-wise, of cameras, is crucial for the comfort of your audience. The slightest vertical parallax must be eliminated, because it would force one eye to look up while the other look down. Various other elements can lead to other painful, disturbing or tiring vertical disparities:

- Cameras are not at the exact same height

- Cameras are slightly pan vertically

- One camera is tilted or rotated in comparison to the other

- There is difference (even if it's extremely small) between the focal length of the cameras. Be careful, some prime lenses (same brand, same model) labeled “10mm”, for example, are actually 9.8mm, and other 10.1mm, for exemple… so you have to test lenses to be your pair of lenses are actually identical. That's one of the reasons that explain why zooming in 3D is difficult: zooms lenses are complex mechanisms, and reproducing exactly the same move of the different lenses inside the zoom lenses is hard.

- Different optical aberrations between the lenses.

Il faut essayer d’éliminer tous ces problèmes au tournage (même si c’est quasiment impossible dans la pratique), en mettant les caméras à 0cm d’entraxe et en utilisant des mires et le moniteur 3D pour régler finement l’alignement. Certains outils logiciels (exemple : Binocle Disparity Tagger) permettent de corriger ces problèmes en temps réel.

De même, on veillera à ce que la colorimétrie et la luminosité des caméras soient identiques. Le moniteur 3D permet de contrôler cela avec précision.