I have three 3D layers imported into After Effects from Photoshop CS5. Each one has its own camera and when you rotate that camera you see the object in 3D. But when I add a main camera to the overall composition and rotate it, the 3d objects appear flat as if they are just on a plane with no depth, where has the 3D gone? Is there anyway to show this using a main camera?
Only one camera can exist in such comps. You need to re-purpose one of the cameras created by the import or delete them, but in any case only one camera can be used and the effect will use it automatically.