How an Automatic Focusing Projector Works

Some higher-end projectors have automatic setup features built-in. These can include automatic zoom, sensing for the color of the wall and even automatic focus. Projector autofocus systems ensure that the projected image is as sharp as possible without you having to focus the lens yourself, giving you one less thing to worry about as you set up for your business presentations.

Automatic focusing projectors have two features that manual focus projectors usually lack. The first is a special motor that rotates the lens elements, letting the projector control its own focus. The second is an ultrasonic rangefinding module that measures the distance to the screen. The two pieces work together to adjust the projector's focus.

The rangefinder in an automatic focus projector emits a sound signal at a frequency above human hearing. It notes the exact time that it sends the signal and listens for the echo after it bounces off of the surface at which the projector is pointed. The projector uses this time information to calculate the distance between it and the screen. It then turns the focusing elements to the correct setting for the distance from the screen.

Generally, a sharper image is better than a less sharp image, but there are instances where slightly defocusing your projector can actually give you better perceived image quality. Every projector has a small amount of space between each pixel. Sometimes, you can see the spaces between them, making it look like the image is projected through a screen door mesh. This "screen door effect" can be particularly pronounced when you use a relatively low-resolution liquid crystal display projector to throw a large image, and slightly defocusing your projector can make it go away and create a smoother and more film-like image.

If your projector lacks autofocus, you can easily focus it yourself. The best way to do this is to project an image with very crisp edges, so that out of focus areas will be immediately visible. Slowly rotate the focus knob or hold down the focus button until the image looks like it is in focus, then go a little past that point so that it starts to come out of focus. Rotate it back the other way to find the perfect focus point.