Human vision doesn't see into the infrared part of the spectrum. But webcams can see near-infrared light, the sort that's given off in remote controls, for example. This becomes really useful when you want to sense motion or do multitouch detection, especially in environments where the visible light might interfere with video detection.

To take full advantage of the possibilities of using infrared light in this way, you need to modify your camera to see only (or mostly) the infrared light in your space. To do that, you need to 1) remove the infrared filter inside the camera, and 2) add a visible-light filter.

Inspired by the demos here and here, I decided to hack a Logitech Quickcam.

Typical webcam, a Logitech Quickcam

Unplug the camera from the computer and look for a screw hole.

Half the shell removed

The Quickcam has only one screw to remove.

Sensor board removed from the housing

You don't need to totally disassemble the camera, but it helps to pull the circuit board, where the video chip is located, loose from the little flanges inside the housing.

Unscrewing the lens from the sensor housing

Now you need to liberate the lens. This camera lets you turn the big ring to focus the lens, which moves it along a threaded shaft. Just keep turning and it will come out. Other cams might not be so easy.

Unscrewed, the lens separates from the housing

Video chip, and backside of the lens assembly

At the bottom of the lens housing, you can see the video chip. Don't let any dust or dirt fall onto it!

Rear element of the lens

To get to the infrared filter you have to remove the rear element of the lens. This gets a little nasty.

Cutting away the housing

In this lens, the rear element is just force fit (or maybe even glued) into the housing. Fortunately the housing is plastic, so it is possible to slice away at the edge until you get down to the clear plastic lens element. Be VERY careful not to scratch the lens. It is so small even a little zit will affect the image quality (which already is not great).

Also, do not remove any more of the black plastic housing than necessary, since you're going to need some structure there when replacing the lens later.

Infrared filter chip inside the lens

Eventually you'll be able to gently pry loose the lens, revealing the square IR filter.

Prying the filter out of the lens

This filter is glass, so prying it loose can end in a mess if you aren't patient. (It looks to me like a good-quality dichroic filter.)

Replacing the back side of the lens

With the filter removed, this lens looks more like a pinhole camera, hmm. Now you can replace the rear plastic lens element you took out earlier.

Making sure piece is flat and snug

Luckily the lens element presses into place neatly. Get it as flat as you can so the image won't be distorted.

Rescrewing the lens into the sensor housing

If you didn't completely trash the threads on the lens housing, you should be able to screw it back into the assembly.

Relocating the lens assembly

As you're putting the cam back together, hook it up and check the video image. You might notice that the focusing ring may have to be turned in farther than previously to get the shot into sharp focus. I had to put the sensor board in a different position, a few millimeters ahead of where it was before. Fortunately the Logitech housing allowed for that.

Black color negative film makes a good cheap light filter

Finally, to make this an IR-only cam, you need to filter-out the visible light. As others (and here too) have reported so cleverly, you can make a filter for the front of the lens out of several layers of fully-exposed 35mm color negative film. (Remember film?)

More here on the infrared imaging tests.