How Night-vision Cameras Work

Showtime After Dark

In the darkness between the golden hours, photographers find themselves with a few options to choose from. There's always the good old flashbulb or the painting-with-light technique of fiddling with f-stops and shutter speeds to let more light in for longer. The problem is, flashbulbs can wash out detail, and relying on longer exposures can really put a dent in your flexibility.

Night-vision cameras and attachments get around these problems by amplifying existing light or working with a different ambient "light" -- infrared (IR) radiation, either from body heat (thermal IR) or from an active IR illuminator attached to the camera. These tools help make surveillance cameras and nanny cams possible -- to say nothing of the applications spies and private eyes might find for them -- but they're just as useful for photo bugs seeking to see the world through eyes of real bugs.

If you think you can just slap some infrared film into your camera, however, I've got good news and bad news. First, the bad news: IR film is sensitive in the near IR spectrum, not the thermal band, so unless you equip an IR light-emitting diode (LED) or some other IR source, it won't be much help after sundown.

The good news? You might want to click away during the day anyway. Nature comes alive in new ways when photographed in IR, because chlorophyll reflects in the near-infrared (NIR) spectrum. Along similar lines, many flowers assume new splendor when captured by cameras tweaked to photograph UV; their pollen and petals fluoresce in the ultraviolet spectrum.

By the way, did you know that digital cameras come with NIR sensitivity right out of the box? It's true. In fact, manufacturers have to build in a special filter to block the IR channel [source: Chen]. Otherwise, it could cause problems, such as autofocus confusion, soft images -- or unintentional peeping through IR-transparent clothing. Some IR still gets through, so you can shoot IR snaps simply by blocking all non-IR radiation with a filter and taking a very long exposure.

If you don't mind cracking open your camera, you can also remove the blocker entirely. Some shops will do this for you. Then, you can either replace the IR filter with one that removes visible light (for an IR camera) or a transparent filter (in which case you'll be able to shoot color, or IR, depending on the filter you put on your lens).

With film or digital cameras, you can always kit-bash an IR flash. Just place a piece of polyester IR filter on your flash and you're good to go.

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