How did the early film projectors work?

Everyone misses the old days. Warm cymbals! The open-air movie begins. This is a warm melody. ...

Anyone who has seen a movie will be attracted by vivid pictures and vivid sounds, and he must also want to know how the movie is shown. To show a movie, you must have film, which is transparent, and many pictures are made by filmmakers with cameras. A movie projector is needed to turn movies into pictures and sounds.

The optical principle of film projector is similar to that of slide projector, which also uses convex lens as lens to enlarge and project the picture onto the screen. But there are many other devices in the film projector to ensure continuous motion. Movies are not shown one by one like slides. In film projectors, people have designed very complicated machinery to make films pass through the lens continuously at the speed of 24 films per second. This kind of projection takes advantage of the persistence of human vision. What the audience sees on the screen is a continuous picture, which feels very natural and has no feeling of flickering and jumping.

Early films were silent, called silent films. A movie with sound appeared in 1906, but at that time the picture and sound were out of sync. Now the audience can listen to the wonderful sound while enjoying the movie pictures, which is the credit of modern movie projectors. When making a film, the sound in the film is also converted into different optical signals and recorded on both sides of the film. The film projector also restores the light signal on the film to sound while showing the picture, and plays it out through audio equipment, so that the audience can enjoy colorful movies.

Generally, movies are shown by projectors, and the pictures seen by the audience are not three-dimensional. Now there is a movie called "three-dimensional movie" to let the audience feel the three-dimensional space. This is two movie projectors showing at the same time, and each projector shows a slightly different picture, which is exactly the same as the difference between people's two eyes (if you close one eye and take turns to see things with the other eye, you will find that the left and right eyes see different pictures). The audience should wear special glasses when watching. Each eye only sees the picture projected by a projector, and the pictures seen by both eyes are reflected in the brain, forming a strong three-dimensional sense and producing an immersive effect.

In order to achieve a certain effect, some special screening forms are often adopted, such as ring screen movies, dome screen movies, image maximization and so on. Now filmmakers are still studying "holographic movies", shooting them with more advanced technology and showing them with special film projectors, so that viewers can get a more real feeling without wearing glasses.