Most digital cameras are sensitive to infrared light. You can check yours out by pointing a TV/video/stereo remote control at the camera, looking in the preview screen and pressing a few buttons. If the camera can pick up IR light, you'll see a flickering white or bluish light in the screen ... with nothing visible to your eyes.
So what? Well, the world in IR light is a different place, eerie and rather beautiful. Worth looking at, in fact. And you don't need expensive and hard-to-get filters (or even more expensive films) to try a few experiments.
The above photo was taken earlier today, with just two pieces of unexposed and developed slide film held in front of the lens. Slide film has the useful property of being nearly opaque to visible light, but will let through IR quite happily; we found that two layers gave the best result when we tried it out. Clip off some sections from the end of the strip, where there's no photographs.
You'll need a tripod, too, or some other way of steadying the camera. Because there's hardly any light getting through the exposure will be much longer than normal; choose a bright sunny day. Using the self-timer helps.
The pictures will probably be rather dark, and will need some adjustment in Photodesk. This shot has had the gamma levels adjusted to brighten it up and increase the contrast a little, and a small amount of sharpening.
Look carefully, and compare it with the normal picture below. Notice the eerily glowing foliage and grass; it emits heavily in near IR wavelengths. The sky is interesting, too -- almost black, with greatly increased visibility near the horizon, showing the haze-penetrating nature of IR radiation. (The just-visible circular object above the car is probably just a dust-speck on the lens or filter.)
One slightly puzzling phenomenon is the opaqueness of the car windscreen. Glass normally lets through IR ... otherwise greenhouses wouldn't work, and this experiment wouldn't either; the lens is glass, too. Perhaps car windscreen glass is specially treated in some way.
Bottom (normal) image:
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