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How Night-vision Cameras Work

Watching Green TV by Starlight, or the Armies of the Night

The roots of military night vision reach back to the 1930s, when research into television technology produced a tube capable of converting infrared images into visible displays. American armed forces based their first night-vision devices, used in World War II and the Korean War, on this Generation 0 technology [sources: Brickhouse; National Archives].

While a worthy first attempt, the bulky Gen 0 scope had problems, like heavy batteries and a beam that might give away a sniper's position if the enemy was packing an IR sensor [sources: Brickhouse; National Archives]. So much for stealth recon.

By the Vietnam era, the army had moved on to Generation 1 devices, aka "starlight" scopes, which amplified ambient light to turn blackish night into greenish day [source: National Archives]. In a starlight scope, light passes through a lens made up of optical fibers, then strikes a photo-emissive element -- a light-sensitive material that converts photons into electrons. These electrons feed into a series of tiny devices similar to TV picture tubes, each one multiplying the image brightness. It's a bit like pointing a video camera at a television, turning up the brightness, and then repeatedly feeding the camera image back into the TV (which probably wouldn't work, but you get the idea). Gen 1 starlight scopes could amplify the ambient brightness around 40,000 times [source: National Archives].

Gen 1 scopes issued in Vietnam were good to a range of up to 500-1,000 meters (1,640-3,281 feet) in near total darkness, but they remained too pricey and awkward to be considered practical for hand-held weapons. Another knock against them: Shooters could suffer brief blindness from flashes sparked by tracer fire or Dragon anti-tank missiles [source: National Archives].

Light amplification continued as the focus with Generation 2 scopes. These lighter, smaller and cheaper tubes replaced the Gen 1 "mini TVs" with a single electronic device called a micro channel plate (MCP), which output as many as 10,000 electrons for each electron they received as input. These output electrons struck a phosphor screen at the tube's viewing end, generating an image [source: National Archives].

MCP scopes were roughly a quarter the size and half the weight of Gen 1 scopes, and they provided both a sharper image and less distortion than their predecessors [source: National Archives]. Their smaller, more compact design also made the first night-vision goggles possible.

Generation 3 got even better, producing MCP scopes with improved resolution and sensitivity. A metal-oxide ion barrier film on the MCP extended its life span to around 10,000 hours, compared to the 2,000-4,000 hours possible with Gen 2 tubes [sources: Brickhouse; Morovision].

Generation 4 devices removed the ion barrier film to diminish halos and boost sensitivity, signal-to-noise ratio and resolution, but a high failure rate spurred the armed forces to retire the designation for the time being. Some companies, somewhat controversially, continue to apply the term, however [sources: Brickhouse; Morovision].

As the army perfected its tech, it continued to trickle into the consumer sensor and photography markets, where other kinds of shooters thought of new applications for the newly accessible wavelengths.