Câu hỏi:

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

THE ILLUSION OF FILM

Film is an illusion because the  moving pictures seen on the screen are not moving at all. A film is actually a series of tiny still pictures, or frames. They appear to be moving because the retina of the  human eye retains the impression of an object for a split second  after  that object has actually disappeared. This principle is known as the persistence of vision. When we look at a single frame of film, the image persists in the brain’s visual center for a fraction of a second. Then, the next frame comes along and the brain has to catch up with the new image. Thus, our eyes and  brain trick us into thinking that we see a smoothly moving image rather than a series of still ones.

Another  illusion of film is known collectively as special effects, the tricks and techniques that filmmakers use when makeup, costume, and stunts are still not enough to make a scene convincing. Special-effects artists apply science to filmmaking, showing us things that no plain camera could ever photograph. Even since the introduction of computer graphics in recent decades, the films of today still rely on some special effects that have existed since the early years of cinema.

One category of special effects is called optical or visual effects, tricks made with the camera. One of the pioneers of optical effects was the French filmmaker Georges Melies, who invented a technique called stop-motion photography. With this technique, a scene is filmed, the camera is stopped, the scene is changed in some way, and then the camera rolls again. Stop-motion photography can create the illusion of an actor disappearing on screen. In one short film, an actor’s clothes keep returning to his body as he tries to get undressed. Melies also invented a technique known as split screen. By putting a card over the camera lens, he prevented half of the frame of film from being exposed. He filmed a scene on the uncovered half of the frame and then backed up the same strip of film in his camera. For the second shot, he covered the exposed  half and took another series of pictures on the half that had been covered the first time. With the technique of split screen, it is possible to achieve illusions such as having the same actor play twins.

Mechanical effects are another category of special effects. Mechanical effects are objects or devices used during the filming to create an illusion, such as feathers or plastic chips to simulate snow, and wires to create the illusion that people are flying. Many sound effects are mechanical effects. Wood blocks create a horse’s hoofbeats, and a vibrating sheet of metal sounds like thunder. During the silent film era, the music machine called the Kinematophone was popular because it could produce the sounds of sirens, sleigh bells, gunfire, baby cries, and kisses—all at the press of a key.

Other  mechanical effects are puppets, robots of all sizes, and tiny copies of  buildings or cities. To reduce the cost of studio sets or location photography, special-effects technicians create painted or projected backgrounds, which replace the set or add to it. For example, in a long shot of a town, the set might be only a few feet high, and the remainder of the town is painted onto a sheet of glass positioned in front of the camera during filming. In a 1916 silent film called The Flying Torpedo, mechanical effects created the appearance of an enemy invasion of the California seacoast. Technicians threw small contact—rigged explosives into toy cities, scattering the tiny buildings into the air. An artist painted a row of battleships on a board that was only six feet long. Carpenters drilled small holes in the ships, which were filled with small charges of flash powder to simulate guns. An electrician wired the charges so they could be fired on cue from a small battery. For audiences of the time, the effect was of a real fleet of ships firing on the California coast.

Sometimes optical and mechanical effects are used together. For the original 1933 version of King Kong, the filmmakers wanted to show the giant ape climbing the Empire State Building in New York City. To show Kong’s climb, the special-effects technicians built a tiny movable model of the ape and a proportionately small model of the Empire State Building. Then, stop-motion photography was used to create the illusion that Kong was moving up the building.

Why does the author discuss the principle of “persistence of vision” in paragraph 1?