How Night-vision Cameras Work

A spooky picture like this, shot with infrared, could be yours if you bust out your camera after the sun goes down.
Comstock Images/Thinkstock

Looking to do a little ghost hunting? In the mood to re-enact your favorite scene from "Predator"? Whatever your pleasure -- from security to nature-watching to artistic expression -- there's a night-vision camera for you.

Nighttime photographers entered the picture in 1871, when Richard L. Maddox developed a photographic plate that was finally up to the task. Early photographers captured images on wet plates -- panes of glass coated with chemicals -- which were touchy and cumbersome and required exposure times that made night photography impractical. Maddox's gelatin dry plate changed all that, becoming the first medium capable of capturing nocturnal cityscapes [sources: Encyclopaedia Britannica; Schwendener].

As time passed and interest spread, legendary photographers such as Alfred Stieglitz, George Brassaï, Weegee and Diane Arbus brought better cameras, improved film and special development techniques to bear. These famed photogs peeled back the curtain of night not with night vision, but with the glow of city lights, illuminated signs, moonlight and the occasional flashbulb.

By the 1970s, Japanese photographers such as Kohei Yoshiyuki were stalking city parks at night, capturing voyeuristic tableaux with their infrared (IR) film and filtered flashbulbs. The era of true night-vision image capture had begun, and both criminals and young lovers would never be safe again [source: Schwendener].

From World War II to today, the U.S. armed forces have driven night-vision tech. As the military turns out incrementally better night-vision scopes, the technology finds its way into civilian cameras. Most prominently, closed-circuit security grew from its infancy in the 1970s to become commonplace by the 1990s [sources: Demetriadi; National Archives; Roberts].

Today, night vision is most widely available in security cameras. Some work only at night, while others switch modes based on user input or ambient light. Surveillance rigs can run from $18 for a 0.5-lux low-light camera to $3,670 for a top-of-the-line thermal imaging model (lux measures the minimum light a camera needs to pick up an image, so lower = better) [source: Brickhouse].

Out-of-the-box night-vision photography cameras are rare. The Midnight Shot NV-1, a dual-mode, digital color/IR camera offered through ThinkGeek for $99.99-$149.99, was the only exception we could find in 2012. In most cases, photographers turn instead to IR film, IR lights and special filters, or hack their digital cameras to capture IR (more on that later). Night-vision adapters for photographic and video cameras offer a simpler approach, but will set you back a cool $6,840-$10,819. Thermal imaging cameras, such as the FLIR T series, break the bank at $8,450-$14,294.

Whatever your shopping selection, your camera will use one of two basic approaches to see in the dark: It will either amplify dim visible light, such as the ambient nightglow of the moon and stars, or gather electromagnetic radiation types that humans can't perceive, such as infrared.

It makes sense that we would end up taking these two approaches; after all, that's how Mother Nature does it.

Burning Bright in the Forests of the Night

Nature abounds with creatures capable of seeing a world hidden from us, a land of ultraviolet-patterned flowers, thermal signals and bright nights. Night-vision technologies borrow tricks from these nocturnal and deep-sea denizens, boosting extant light or peering into infrared realms.

When it comes to seeing in low light, the eyes have it, thanks to a slew of specialized adaptations, including larger eyeballs, bigger lenses and pupils that open extra-wide -- all of which add up to more light entering the eye. Some dark dwellers' retinas bristle with many more rods (highly light-sensitive cells) than cones (detail and color receptors). Others lack cones altogether or feature rods specially built to maximize light-gathering.

The retinas of cats, cows and other animals feature a kind of mirror called a tapetum lucidum. This reflector bounces light back through the light-sensing cells of the retina, increasing the "brightness" of the image by boosting the nerve signal to the brain. Some say that this is why cats often have creepy glowing eyes in photographs (but I'm pretty sure it's actually because they're gazing into your immortal soul).

Some animals perceive wavelengths of energy that human eyes cannot. People see the world trichromatically, building a color image by combining signals from three kinds of light sensors, each tuned to a different wavelength within the 390-750 nanometer band: short (blue), medium (green) and long (red), with signal receptions peaking at 445 nanometers, 535 nanometers and 565 nanometers, respectively.

Bees are also trichromats, but one of their light-sensing cell types is tuned to the ultraviolet spectrum (peaking at 360 nanometers) [source: Meyer]. Some flowers and pollens display stunning patterns in this range; it's nature's club stamp, viewable only under black light, and it grabs bees' attention [sources: ASU; Deriso].

Rattlesnakes sport sensory pits capable of "seeing" radiation in the thermal infrared spectrum, which means they can spot a warm-blooded animal based on its body heat [source: NASA]. Predator, indeed.

When humans began developing night-vision technology, we adopted two of these approaches: light amplification, also called light intensification, and thermal infrared. We've also dabbled in near-infrared.

Humans radiate most strongly in the infrared in the 10-micrometer band, so thermal cameras typically operate in a range of around 3-30 micrometers [source: Morovision]. Within this wavelength bracket, warm objects -- such as vehicle engines, fires or people -- stand out against background heat, particularly at night -- a fact the U.S. Army would soon take advantage of.

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.

Seeing With New Eyes

With thermal infrared, it's pretty easy to see the areas of this house that are losing heat. The brighter colors represent areas of heat loss.
With thermal infrared, it's pretty easy to see the areas of this house that are losing heat. The brighter colors represent areas of heat loss.
Alfred Pasieka/Peter Arnold/Getty Images

Night-vision cameras boast uses beyond commercial security, public safety, military operations, spy games and checking up on the hired help.

In industry, thermal infrared (TIR) can detect hot spots in circuits, pumps and other equipment, see heat loss, identify signs of water leakage and termites, and allow supervisors to check liquid levels in storage tanks without even popping the top [source: Seidner].

Ultraviolet has been kicked around as a possible night-vision source but, like near-infrared (NIR), it requires an active illuminator. In terms of active night vision, NIR covers the same bases as UV with fewer drawbacks and a longer pedigree, so it remains the standard choice. Still, UV provides an example of how looking a little beyond our visual range can reveal a great deal about our world that light amplification alone cannot.

Take coronal discharge, or corona, for example. Corona refers to a partial release of electrical energy around an energized conductor, such as an electrical transmission line. In essence, it's a visual tip-off that you're losing energy, probably because of the conductor's voltage, shape and diameter, surface irregularities such as scratches and nicks, or dust or water drops [source: California Public Utilities Commission]. Corona often blares ultraviolet; by tuning in to the Solar Blind UV band (240-280 nanometers) -- a wavelength window of opportunity created by the atmospheric absorption of solar UV in that range -- special cameras can detect this telltale UV even in daylight [source: SBUV].

Like your in-laws, thermal IR is very good at finding faults, so industry uses thermographic monitoring to examine fusion reactors, check circuitry and unravel engineering problems [source: American Society for Nondestructive Testing].

If saltwater runs through your veins, night vision can save you a few trips to the crow's nest -- and identify a few hazards your radar might miss. Night-vision cameras can help detect buoys, rocks or outcrops, as well as small vessels, whereas thermal IR can spot oil spills, icebergs or even approaching pirates [source: FLIR].

NIR cameras have infiltrated a number of fields as assaying tools, largely because, unlike typical chemical analyses, they provide nondestructive, cheap and instantaneous analyses without having to leave the site [sources: ASD; Batten]. Botanists use NIR reflectance to gauge levels of nonstructural carbohydrates in plant shoots, a sign of plant stress [source: Batten]. Rock hounds, prospectors and geologists employ shortwave NIR to analyze mineral deposits on-site [source: ASD].

As for the police, the fuzz is all abuzz with NIR. Law enforcement applies the tech to detect counterfeit drugs and to reveal altered documents and forgeries [sources: Rodionova; Somma].

Satellite instruments rely on many of the same sensors to spot key features on the Earth. Under NIR, chlorophyll sparkles like Edward Cullen in sunlight, so it provides an easy way to map vegetation [source: NASA].

When it comes to finding amazing subjects for night-vision photography, however, you don't even need to leave your backyard.

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.

Author's Note: How Night-vision Cameras Work

Growing up, I was captivated by various kinds of vision, from the world-tinting wonder of cheap transparent plastic to the insectlike, compound-eye effect of kaleidoscopes. I wandered rooms of funhouse mirrors, clicked through View-Masters and collected and constructed optical gadgets small and large, from cheap microscopes and telescopes to pocket-sized periscopes.

My foray into night vision began with an ill-advised high school trek into an unfamiliar part of town to find a security retailer. My friend and I were full of beans and on a mission: he, to check out the "spy" gear, and me to look through a night-vision scope. Had we given the matter any thought, we would have assumed that the sales staff would take one look at our teenaged faces and give us the boot. To my surprise, though, one of the staff took me to a darkened demo room and let me peer through one of the shop's several-thousand-dollar scopes.

Once I'd gotten over the fear of breaking the thing, I was swept up in the marvel of seeing my own hand in pitch-blackness. I still recall it vividly: The lack of parallax and the odd, invisible-flashlight greenness of it combined to make me feel oddly disembodied.

I first encountered daytime UV and IR photography while writing another HowStuffWorks article, How to Capture Winter Scenes in Photography. As I surfed around the Web looking for experts on the subject, I came across landscapes that looked to be covered in frost and rime, but were actually the product of IR reflecting brilliantly off chlorophyll-packed leaves and grass. Ever since then, I have been obsessed with the idea of experimenting with IR and UV photography.

I think the desire to see the world differently -- both literally and metaphorically -- is a natural tendency, and a useful one, for artists, scientists ... anyone, really. Now, if you'll excuse me, I need to find a pawnshop that sells digital cameras on the cheap; I have some IR blockers to hack.

Related Articles


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