When the movie started, at first I was disoriented by the 3D because I could only focus on one element of the scene, and if I tried to look at the background I could only see a blurred image. I understood almost immediately that this was intended by the creators, and it helped me a lot through the movie: the movie director wants you to look at a specific object, character or field of vision, and enforces it by keeping only that particular target focused, and leaving the rest unfocused. In a sense, you must enjoy the experience that the director prepared for you, and understand that you have no freedom to do otherwise; be aware that this is not as bad as it sounds, because they really know their stuff. An example is the second scene, where the protagonist is in the foreground and two military officers are in the background: I wanted to see the officers’ faces but couldn’t, because they were too blurred; this was not an issue at the end, because those two people were never seen again in the entire movie. So the rule is:
If you can’t see it, you don’t need to see it.
At one point I tried to adjust the 3D glasses on my nose, pushing between the lenses with my finger. In that moment I lost the 3D vision and the images appeared too bright and doubled; the correct behavior was reestablished a second after I removed the finger from the glasses. The reason for this is the presence of a sensor on the front of the glasses, between the lenses. This sensor communicates with a transmitter placed near the cinema screen, and receives a signal that is used to create the 3D effect. This is roughly how the 3D technology works:
The projector creates alternatively two images on the big screen: one must be seen by the spectator with the right eye, while the other must be seen with the left eye. To enforce this requirement the special glasses impede the view of the right or left eye by rendering their lens opaque and transparent alternatively. Our brain cannot perceive this switch between right and left eye because it is very fast: 120 times a second, which is 60 frames per second for each eye. To be sure that the right lens is opaque and the left lens is transparent when the projector is showing the left image (and the other way around), a synchronism must be applied between the projector and the glasses. This synchronism consists of a signal sent by the theater system to the glasses of all the spectators. By interrupting this signal both lenses become transparent and the spectator sees both images on the screen.
I think that having a basic understanding of the technology behind 3D cinema would help improve the user experience. When I got out of the cinema I overheard people saying “It was too blurred” or “Sometimes the 3D disappeared”; if those people knew these facts, maybe they would have enjoyed Avatar more: it is an awesome movie, created with an awesome technology.