This page is constructed from other blogs and articles that I have written, so may be a bit jumbled. I hope to cover some of the key points of shooting in 3D.
CAMERA SYNC.
Getting the two cameras in sync for 3D is crucial if anything moves in the shot, especially if anything is moving across the frame. Imagine a shot with a car traveling through the frame. If the cameras are not completely in sync, the position of the car when the image is captured will be slightly different for the left and right views. This will in effect move the car forwards or backwards in 3D space as the cars positional difference between the left/right frames will alter the convergence/divergance for the car. The static parts of the frame will be unaffected. Imagine also a shot of a person walking or running, if one camera takes its shot slightly behind the other, the persons legs will be in a different part of their stride so the left eye will see legs in one position while the right eye will see legs in a slightly different position and the 3D will break down.
Also consider what happens when you pan. If one camera captures its image slightly ahead of the other then the 3D depth will appear to either compress or expand as the cameras are panned because the left and right images will be shifted slightly left or right with respect to each other. Even at 30 frames per second a half frame sync difference would equate to a half degree difference between the 2 cameras with a 5 second 180 degree pan, which is not all that fast.
It’s not just a case of getting the cameras to go in to record together, as the it is the video streams that the cameras are producing that need to be in sync, so you need both cameras to switch on and power up in sync.
At 24P (the slowest typical frame rate) it is traditional to use a 1/48th shutter. To ensure that both cameras are exposing for at least half of the open shutter period together they must be within roughly 1/100th of a second of each other. This is the absolute minimum needed and wont be ideal for any fast movement. Ideally you want cameras running within 1/1000th of a second of each other. This can be achieved with a Lanc controller or genlock.