Seeing the world in a new light

I’ve just been massacring my old webcam. Aside from the general catharsis of sticking a knife into a rather cheap relic of webcams past, the intention was to convert the PC Line 300a from a poor visible light capture into a poor infrared light capture device.

The general principle of converting a web or any other digital camera, comes from this webpage. Every CCD device is capable of recording infrared light (try pressing your remote control and looking at the front of it with your phone camera) and to stop this from interfering with the image obtained, the cameras come with IR blockers. This is the reason for the red tint when the lens catches the light just right. Somewhere, either on the CCD or by the lens itself, there is a square of glass that is to some extent opaque to infrared light. In the case of phone cameras, not that opaque as it would cost more, in the case of higher end CCDs, very opaque.

The steps to converting the camera from visible to infrared light come in two stages, therefore. Firstly, we have to remove the infrared blocker, to allow as much IR as possible to hit the CCD. Then we have to block out the visible light to ensure only the IR hits the sensor.

The first step is to get the lens out of the camera. For the PC Line 300a, this is easy. Focusing is achieved by turning the lens in its thread. Turn it one way too much and it drops out. Then comes the problem. Behind the lens array is the CCD on the circuit board – but no IR blocker. That is embedded in the plastic that makes the back end of the screwthread.

This I tackled with an old Woolworth’s multitool (you may have to improvise…). I filed away part of the back of the housing and picked away at the rest until it yielded the square. I then popped it out and dropped it in the nearest bin. Then I took an old exposed film and cut two new squares of the same length and width as the old blocker. These were placed into the housing in the same position as the old IR blocker to act as the new visible light blocker. Then I screwed the thing back together again and took a couple of pictures of me in a black t-shirt, holding up an illuminated phone display and a remote control, initially without pressing anything and then after a press… you can see the results.

Interesting though this may be, what is the point (beyond a demonstration of light beyond the physical spectrum to be done as part of activities at the young astronomer’s club this month at Kendal Museum, 17th of July)? Well some optical effects such as rainbows have a strong associated infrared signal and it just gives another interesting way to photograph the world and look at it.


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