Headaches, nausea, dizziness from stereoscopic viewing — caused by convergence-accommodation mismatch. Often results from poor depth budgeting or miscalibration.
Anyone shooting in 3D knows the problem: audiences leave the cinema with headaches, some report dizziness or nausea. This is no coincidence, nor is it a filmmaking error in the classic sense – it's a physiological reaction to conflicting signals that the eyes and brain have to process. The conflict arises because the eyes focus on different planes, while the convergence (the axes of the eyes) points in a different direction. Your eye wants to look both near and far simultaneously – this leads to strain, fatigue, and in sensitive viewers, the classic symptoms of 3D Sickness.
In practice, this usually happens due to faulty depth budgeting. If you set too aggressive positive or negative parallax – meaning you place objects too far in front of or behind the screen – you force the eye into extreme convergence angles. It becomes particularly problematic if the zero-parallax point (the plane where both camera images are congruent) jumps constantly or is set completely incorrectly. I've seen productions where the DP hadn't calibrated the stereo baseline – the result was unwatchable. Motion control errors can also trigger this: if the two camera series don't move perfectly in sync or the convergence isn't adjusted smoothly enough, visual noise is created that the brain perceives as disturbing.
The practical remedies are simple but time-consuming. First: convergence and baseline must be checked individually for each scene. Don't just set them across the board. Second: the depth budget must be conservative – better to stay subtle than to become too spectacular. Third: aggressive 3D cuts should be avoided during editing; cuts within the same depth plane significantly reduce discomfort. Fourth: test screenings are not optional, but mandatory. If ten percent of the test group reports complaints, you have a real problem. And finally, as a DP, you should have a monitoring system – not just the on-set checker, but also regular quality control of the final stereo composition, ideally in the cinema itself, not just in the DCP preview room.
3D Sickness is not an inevitable fate – it's a sign of technical negligence. Those who respect the rules will overcome it.