Craig Houghton September 7th, 2007
I’ve been meaning to post about this, but I’ve been ill. I find the nearly visible endlessly fascinating, so I’m sure I’ll return to this topic soon.
Near-infrared light is just beyond visible red light. With wavelengths of 780nm and up, it’s a spectrum we’re just not built to see. Well, there is a bit of an overlap, but the visible light around us overpowers the narrow band we can see without technological assistance. Near-infrared is the channel-changing bright light your remote control shines at your tv box. Take a look. If you can’t see the light when button-mashing (and, you shouldn’t be able to), look at it through your digital camera viewfinder. Note that this isn’t heat-based thermal vision and it isn’t infrared boosting night-vision, but it’s very cool.
See the links below for more on this, but the short story is that most digital cameras have a filter to block infrared light. They’re not out to spoil your fun — it helps to improve your pictures. However, it’s often a weak filter that still lets through some infrared light. However, whatever filter is there still acts like a pair of infrared-blocking sun-glasses, so you’ll have to use a looong manual shutter speed or set your camera to nightshot.
Learn more:
Infrared goggles ($10)- milk that narrow band of near-infrared that we can actually see (yes. they work.)
same idea with less talk, more pictures
use old film/exposed negatives to make an IR filter - that works, but the $30 dollar filter I bought for my digital camera 
worked far better. try the home-made filter method if you can’t buy a real IR filter for your camera. there are some tutorials out there (and there are many) that use floppy disks instead of exposed negatives. the floppies I used just wasted my time and made everything rather dark and smoky
remove the internal IR filter to increase sensitivity - most digital cameras (and probably webcams too) will do just fine with their internal filter intact, so I wouldn’t reach for that screwdriver yet
As for me, I’m very happy with my purchase of an Opteka 58mm 720nm Infrared Filterfor my Sony DSC-H1 digital camera. I’m sure there are other more IR sensitive cameras out there, because I have to keep the camera shutter open quite a while to let in enough IR light for a decent picture. This usually means about 2 seconds of exposure (auto white balance with manual shutter of 2 seconds). Of course, I have to use a tripod at that setting. And, (assuming you’ve been doing some reading elsewhere) no I haven’t seen clothing turn to Saran wrap. Then again, I haven’t really tried, wouldn’t recommend it, and doubt that someone, sun-bathers aside, could hold perfectly still for the required 2-4 seconds. Here’s what I have seen of the ‘invisible’ and beautiful world of near-infrared.
(all photos here taken with my sony dsc-h1 and opteka ir filter)
the photos often look best when tweaked to grayscale. before adjusting, you can get some funky colors
chlorophyll, like in these normally dark leaves, shows up as a strong white in near-infrared
it’s hard to read this photo, but the tree in the center here is a purple plum. the leaves are very, very dark, but they’re white when using a near-infrared filter. the sky also turns dark unless it’s overcast. barely visible clouds and rainbows are easier to see as well.
in near-infrared, a clear sky can be dark like this without after-tweaking
infrared in grayscale (at top) versus visible light in grayscale (below)
the dark plum looks almost like a negative, but it’s not. here’s the visible (bottom) full color along with what an actual negative would look like (at top) just as a reminder. notice that it’s quite different from the infrared atop the first pair.
Also, I really do recommend the $10 goggles (cost a bit more with mail-order parts). When the light is strong (noon till 3 or so on a bright day), it’s a world of pink and white leaves, dark networks of branches, and black skies. We only see a narrow band, but I know it’s the real thing as the plum tree turns a white I could never get with normally-visible light interfering.
