How Autofocus Cameras Work

By: Gary Brown

How Do I Know Which Autofocus System My Camera Has?

Look at the type of camera you have:

  • If it is an under-$50 point-and-shoot camera or one of the single-use, disposable cameras, it is definitely a fixed-focus camera with no focusing system of any kind. This type of lens has its focus set at the factory, and it typically works best with a subject distance of about 8 feet. Four feet is about as close as you can get to the subject with a fixed-focus camera. When you look through a fixed-focus camera, you typically do not see the square brackets or circles found in an autofocus camera. However, you may see a "flash ready" indicator.
  • SLR cameras with interchangeable lenses typically use the passive autofocus system.
  • Cameras without interchangeable lenses typically use active infrared, and you can see the emitter and the sensor on the front of the camera.

Here's a quick test to tell which autofocus system is in use in your camera (some cameras may have both systems):


  • Go outdoors and aim the viewfinder at an area of the sky with no clouds, power lines or tree limbs. Press the shutter button halfway down.
  • If you get a "focus okay" indication, it's an active autofocus system.
  • If you get a "focus not okay" indication, it's a passive autofocus system. The CCD cannot find any contrast in a blue sky, so it gives up.