The built-in microphone on your camcorder can’t be beat for convenience. It’s always there, it’s always on, and it’s always pointing at what you’re filming.
Unfortunately, camcorder microphones have several disadvantages. For example:
They’re usually mounted right on the camera body. In quiet scenes, they can pick up the sound of the camcorder itself—a quiet grinding of the electronic motor, or the sound of the lens zooming and focusing.
If your subject is farther than a few feet away, the sound is much too faint. The powerful zoom lens on modern camcorders exaggerates this problem. If your subject is 50 feet away, the zoom may make it look as though you’re right up close, but the sound still has to come from 50 feet away.