Simple IR Filter using exposed film

A friend is doing a project that involves building a robot that finds and blows out candles placed within a course. They are thinking about using an infra red filter on a webcam to locate the candles, and asked me for suggestions. I know one could purchase filter sheets that serves this purpose, but thought there must be cheaper options/quicker options. First I thought about using red/dark red coloured cellophane, as the frequency is close enough to infra-red and maybe with enough layers it'll block out most visible light. Also, where to find the right coloured candy wrappers? Arts and crafts stores? There MUST be a cheap and simple way to get an infra red filter... (without having the crack open a TV remote or a Wii-controller - all these devices have infra red filters on the front).

After a quick google and 2 minutes of tinkering, I sent an excited message back to my friend with the following images:





The solution: Exposed film negatives!! It turns out developed film that has been exposed to light is a great infra red filter. The bit at the beginning of the roll is usually exposed when you put it into the camera, unless you load it in the dark. (I remember sometimes trying to do this under a blanket to save the first few shots of a roll... this way a roll of 36 can get you 38~40 shots, if you're lucky). You can see the tea-light candle and the film strip in my hand in the above image. And here is what the captured image looks like with the film strip taped onto the front of the web cam:






The solution was so quick, cheap and simple that I had to post about it, right away! :-)

Now the problem of course is the lack of availability of film these days... luckily I kept all my photos/negatives from before...

Credits to here and here.