Infrared cameras for the masses

Well that’s interesting. It seems, mobile phone cameras are actually sensitive to near-infrared light. It really does work. I tried it with my own. Near-IR shows up as a purplish colour. You can see it on anything hot enough to glow or almost glow.

It’s also evidently the reason why any pictures taken on phones involving fire look bleached out and over-whitened. The purple colour would blend with the orange of the flames. Which is, interestingly, a similar effect to the way optical brighteners work in washing powder. But I digress…


This image is of an electric hob, just reaching the temperature where it would glow red. It’s on unapproved personal loan (in other words, I yoinked it) from Built on Facts, where you can read more about all of this…

Interestingly, it kinda makes sense. Without going into the gory details of the photoelectric effect, the sensors in most phone cameras use Charge-Coupled Devices (CCDs). The simplified picture is that photons hitting the CCD array cause charges to build up in different places. Those charges are proportional to the intensity of the light hitting them. Electronics essentially convert those charges into voltages and store the whole thing as a 2-dimensional image. Ok, so that’s very much simplified, but like I said, I don’t want to go into the details right now.

CCDs are used in a lot of places, incidentally — including telescope optics where they’re used to pick up frequencies from infrared right up to UV. While trying to do astrophotography with a phone camera is just plain laughable, I can’t help but wonder what the sensitivity range is on them. I might have to do some experimentation…

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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12 Responses to Infrared cameras for the masses

  1. Anonymous says:

    Interesting…

  2. Anonymous says:

    Happy Geek Day to you too! I love that diagram. I am most definitely a geek.

  3. invaderxan says:

    It opens up a whole new world of micron-wavelength fun! :P

  4. invaderxan says:

    I guess it’s easy to forget and just treat the stuff like regular film, huh?
    And yeah, it does make sense that it could be purely software correction…

  5. That’s pretty neat! I didn’t realize this. Now I’m tempted to do some experimental picture taking of my own.

  6. madsophia says:

    I have a bunch of infrared film in my fridge and I JUST now remembered that I have a roll in my medium format camera that has been sitting by a window for months. I am a moron, it is probably completely fogged from heat.
    anyway. the biggest difference I can think of between your cell phone and your digital camera is their internal software and abilities to do exposure compensation at a more sophisticated level.

  7. invaderxan says:

    Hmmm… Like I was saying above though, unless it’s to do with the electronics, phone cameras seem to be especially bad at photographing fire — which I’d have thought might be to do with them being more sensitive in the IR than most digital cameras. I’ve taken fire photos with a lot of different cameras, and while they look a bit bleached on almost all digital ones, the effect is especially pronounced on phone cameras. Perhaps larger digital cameras come already fitted with a layer to screen out some excess infrared.
    I was guessing it probably wouldn’t be over a micron if even that high. Still, it’ll be an amusing little distraction at any barbecues I find myself at! :)

  8. invaderxan says:

    Haha! GMTA. That was actually the first test I did to see if it worked! :)

  9. invaderxan says:

    The funny thing is though, I’d always noticed how phone cameras are especially bad at photographing fire, while most digital cameras fare a lot better. It seems perhaps they’re a bit more sensitive than most — either due to having thinner lenses or different CCDs. Or maybe other cameras just compensate somehow.
    Deep red… I still haven’t played with any infrared film. I really really should! :D

  10. Anonymous says:

    Most digital camera sensors are sensitive to the near-IR although off the top of my head I can’t remember how far into the IR they go. I suspect it’s not even as far as 1-micron. You can buy IR filters for digital cameras and lots of people use them, but I’ve never been that impressed with the pictures.
    Using a remote control to test your camera is a good idea, point it at the camera and press a button. Your camera should see it (mine does).
    2.5 microns or thereabouts is probably an upper-limit as the glass in camera optics will likely block the IR radiation beyond that wavelength – not that your average cell phone camera sensor will work that far into the IR!

  11. The other neat trick with these is to use your digicam to see if your remote (or other IR-emitting device) is working. Just point the thing at the camera, push a button – and if you can see the red light, it works!

  12. madsophia says:

    my understanding is that many digital cameras are infra-red sensitive. I have heard of people permanently blocking other wavaelengths on DSLR’s.
    also, deep red filter can block out almost everything but infrared.

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