Have you ever seen any 3D movie? Nowadays you can see 3D movie at a lot of place in Japan. And when you see 3D movie, you must be interested in the amazing 3D images.
Why do you see the movie in 3D?
First of all, let think about why a human can recognize in 3D.
Let see... You must have two eyes separating about 7cm. This is the reason why you can see in 3D. When you look at a object, your left eye and right eye see a little different image. Your brain calicurate real 3D image with these different images between left image and right image.
When you see a general photograph or TV, you see one image with your two eyes. So you are too difficult to image in 3D by them. So why should we do to display in 3D?
Stereo photograph is the one of the answer.
There are any method to take stereo photograph such as using a stereo camera or 2 camaras, a beam splitter...etc. In this page, we think about using 2 camera. It's very easy way to understand stereo photograph.
Refer to the following Fig. Place two cameras separating about distance of your eyes. And take photographs by the two cameras at the same time.
Then, after developing, You see the photo taken by left camera with your left eye, and see the photo taken by right camera with your right eye. So The left image go into your left eye, and the right image go into your right eye. And your brain calculate the difference of the images, when you will image real 3D space as you stand the place where you took the photograph.
We use this amazing method for making a map, researching geography, exploring another planet....
Also using two movie camera means it's able to take 3D movie. In many of 3D theater, the left image of movie and the right iamge of movie are projected to one screen by each movie projecters with polarizing filters . And people wear 3D glasses that have polarizing filters when seeing the movie. So the movie projected from left projecter go into your left eye, and the movie projected from right projecter go into your right eye.
Do you understand my explanation?