Cinema is a cross between a camera and the mechanics of a sewing machine, which helped capture on a long strip of film, a large number of photos one after the other. In this instance, since 1927, it is still 24 frames per second.
These photographs projected behind each other so fast, give the viewer the illusion of movement. Just like a book whose pages we turn out very quickly, with a slightly different design on each page, which gives us the illusion of its movement (due to a cognitive phenomenon known as the phi effect).
The cinema is facing a very simple technique reality, which was the main difficulty of its development in the 19th century: it is necessary that 24 times per second, the film is set in front of the camera lens, but must also , 24 times per second, the film can advance to the next picture. If the film advance while light impresses the film, the image will be ’spun’, formed by vertical lines. This is wrong. So the solution is that, for 1/48th of a second, the image is fixed to the camera lens and the light passes to impress the film. Then, during the 48th second of a second, the light is obscured, and the film scrolls to the next image, which in turn will be impressed.
The cinema projection works on the same principle: 24 frames per second. During half time, the light passes, the other half of the time the light is turned off, so that the film scroll to the next image. So, in a cinema on the screen, there are images that during half time. The flashing is not visible to the human eye due to retinal persistence. But in reality, in a movie theater, we are half the time in the dark.
The object that allows that there is light during half time is called the shutter. It is a single disc, half of which is hollow, which runs behind the lens. This disc is synchronized with the movement and stop the film, thanks to another primary object of the cinema, the Maltese cross.
At the beginning, when he was silent, the rate (number of frames per second) was 16 or 18 frames per second. These still images, chained at that speed on a screen, giving the illusion of a natural movement. The phones are still often videos at 15 frames per second.
The film, for the sound quality, increased to 24 frames per second in 1927.