You can sometimes "see" infrared via this simple experiment, using a camcorder with a TV monitor attached. Point the camera toward a TV remote control. Push some buttons on the TV remote control and the camera should "see" invisible infrared light from the remote control. Camcorders typically use CCD imaging chips. These chips are sensitive to infrared light. That's why your camera shows a white spot where the remote's infrared source is located. A "spy" can take pictures in complete darkness if they illuminate the scene with bright infrared light.
Autofocus Video Cameras
Autofocus in a video camera is a passive system that also uses the central portion of the image. Though very convenient for fast shooting, autofocus has some problems:
- It can be slow to respond.
- It may search back and forth, vainly seeking a subject to focus on.
- It has trouble in low light levels.
- It mis-focuses when the intended subject is not in the center of the image.
- It changes focus when something passes between the subject and the lens.
Autofocus video cameras work best in bright light. Switch to manual focus in low light.