Stage plays, at first, seem a lot like films. Both use actors and dialogue and scenery. But if you try to make a film by setting up a camera in front of the stage, you will find it won\'t work. A film made in this way will leave the audience cold. And even worse you\'ll b3e wasting a powerful tool --- the camera.
A stage is actually a box. One side of the box has been removed so the audience can see what\'s going on inside. The actors remain at a fixed audience. In the film, however, the camera can bring the audience up close and fix their attention on small but important things: a frightened look, a whisper, a trembling of hands.
The camera offers the film maker freedom allowing him to move easily across barriers(界限) of time and space. He can show his action in real cities and on real farms. He can also use the camera to change the scene dozens of times in one film. No expert of the stage can do this.

The main idea of the text is that ________ . ( )