What are the problems and limitations of modern 3D? I'm not going to claim any particular expertise in this subject past a decent familiarity with 3D computer graphics. However I do think that there are a couple of key points that are passing people by in the recent excitement about 3D cinema. The pedant in me wants to go on record ;-).
The main thing that is not being said is that the 3D we are experiencing is solely 'Stereoscopic 3D' this means that everyone in the audience is seeing the same 2 images for every frame of the movie.
The best way of highlighting the limitations is to point out the differences in experience between real 3D (i.e. the world around us) and the 3D we experience in the cinemas.
While we do experience the world through two eyes those eyes do have to a degree the ability to sense distance individually through their focus - we do not completely rely on the stereoscopic effect to determine distance and so never lose the ability to determine how far away something is even if we were to lose an eye. This means that the illusion can never be complete as the focus in a 3D movie is determined by the director and camera departments. If something catches your eye that is not in the plane of focus then all you can ever see is a blur though your eyes may strain to focus it. This is both a blessing and a curse as it provides another tool to the director to direct your attention within the frame but can also wreck the illusion.
Another issue is that the stereoscopic effect is achieved by filming the scene from a fixed viewpoint. This means that the frames captured look best from a specific place in the cinema. The further away from that position the less effective the 3D effect is.
A related issue is that the illusion requires one orientation of the spectator. If you lean your head to one side the illusion starts to dissolve as instead of seeing the frames for the top eye and the bottom eye you will keep on seeing the frames for the left and right eyes. This gets worse if you were to continue the rotation as the eyes would then be reversed... Not many people will see the movie standing on their heads but couples leaning their heads on each other's shoulders will have a problem.
The final issue is that of movement. In dealing with a 3D world we are used to moving around it and seeing different perspectives. Despite the fact that we are largely fixed in our seats in a cinema we still have the impulse to crane up or slump down, lean left or lean right just to see that little bit more. Unfortunately the Stereoscopic 3D effect cannot handle that behaviour.
It worries me a little that there is talk of bringing Stereoscopic 3D into the home as there may be an effect where people are trained to sit absolutely still in one orientation to maximise the effect. There are already concerns about how children sitting still in front of the traditional 2 D television and not fidgeting are contributing to the obesity epidemic, how much worse may it become with Stereoscopic 3D TV?
