Since it was created, cinema has evolved a lot, gaining sound, colors and special effects. The latest novelty are 3D films, which need special glasses, like the one below, to be watched.
In 3D films, the scenarios, the people and even the cartoon characters can be visualized three-dimensionally, as if they were real and were closer to us. Thus, the idea of the producers of these is to “deceive” our brain and our eyes, making them think that they are in front of a three-dimensional space and not in front of a common two-dimensional screen.
In order to understand the functioning of 3D cinemas, it is essential that we know that human beings have binocular vision , so that each eye sees a different image, and the brain is responsible for combining them into a single image.
The angular difference (almost imperceptible) between these two images, called deviation , is used by the brain to help in the perception of depth. It is precisely for this reason that when people lose sight of one eye, they also lose their spatial notion.
Ancient 3D film productions used anaglyphic images to take advantage of binocular vision and deviation. These images include two layers of color on a single strip of film reproduced by a projector, one layer being red and the other being blue (or green).
Thus, when we wished to watch these films, it was necessary to use a 3D glasses with a red lens and a blue (or green) lens, like those in the figure at the top of this page. These lenses “forced” one eye to see the red section of the image and the other, the blue (or green) section.
It is due to the differences between the two lenses that the brain interprets them as a three-dimensional image. However, due to the use of colored lenses, the coloring of the “final image” is not accurate, so there are data that report that this technology has brought many problems for people such as headaches, eye injuries and nausea.
For this reason, another technique has become more widely used, which is the polarized mode . Although it is more expensive and complex, it is more faithful and maintains the original colors. Each image is projected with a different polarity (sometimes with two simultaneous projectors). In this technique, glasses with special lenses are also required for visualization. Each lens of the glasses has a different polarization filter: one lens filters the polarized waves vertically and the other horizontally. As the polarized lens darkens the images a little, the projection screen is silver in order to increase the brightness of the image.