Military Police Photo
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 CT PHOTO ato 637 WWII Bougainville Military Police  US $9.99
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 Military Police WWI Photo 1918 PF US $8.89
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 MILITARY AUSTRALIA REAL PHOTO VIETNAM WAR 35 SECURITY POLICE SQUADRON SENTRY DOG US $18.36
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 1973 Press Photo FERNAND LEGROS ART DEALER HELD MILITARY POLICE US $21.88
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 1942 Press Photo Military Police S A Wood machine Plant US $18.88
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 1915 Press Photo Military Citizen Police US $28.88
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At the mention of night vision devices, images can come to mind like spy and action movies, soldiers scouring an area with the device at night, helicopters hovering overhead aiding the police in tracking fugitives or detectives using the device to spy on people they were assigned to track.
Night vision devices are actually light enhancing and thermal imaging tools. It makes a particular subject visible by the warmth it emits or observable by using limited light. It enhances a spectral range making the viewer see lights and images that would otherwise have been invisible to the bare human eye. The normal human eye is capable to seeing images that are confined to a certain electromagnetic spectrum that the brain interprets. Night vision devices may use another source of light that enhances images enabling the user to detect objects that improves the detection capacity of the normal eye.
In theory the human eye can see these weaker sources of lights but the brain has a way of filtering out these lights that we are only capable of seeing a very limited number of photons. With the aid of a night vision device, these photons intensified by the photo multiplier tube enables us to see different colors of lights in a subject. When seen though and NVD, an image that is nearly invisible becomes observable.
Many animals have this capacity to see through the dark. Animals that can hunt at night uses a larger optical aperture, an improved composition in the retina, optics that are more photo-efficient that enables them to use weak lights and see better in the dark.
Night vision devices that most people are familiar with are the night vision goggles. This night vision device has an image intensifier that converts weak lights from the near infrared spectrum to visible images that enables the eye to see objects as far as 200 feet in near complete darkness. This night vision device displays a green image because the peak sensitivity of the human vision is near the green range. It also uses two different technologies depending on your choice of the night vision device.
One uses the Image enhancement where the night vision device enables the viewer to see images by collecting tiny amounts of light that may already be imperceptible and amplifying it to make the image visible. The other is through thermal imaging where the heat emitted by the subject is used and translated into images. The principle is that hotter objects tend to transmit more light than the cooler ones like stones and trees.
Night vision devices were originally intended for military use to aid them in tracking down an opponent at night. It has evolved now into many different uses.
Lately night vision devices are finding use outside of the military and police detection work. When you are out camping, night vision devices could prove very helpful. Businesses have also been installing night vision devices within and without their properties to enable them to observe if something has been touched or changed during the night. Night vision devices are also proving to have invaluable aid in detecting soil that have been disturbed, buried objects, footprints and almost anything that needs to be determined in instances where there is very limited lighting.
Some of the more common applications for the night vision devices are entertainment, hidden-object detection, hunting, law enforcement, military, navigation, security, surveillance and wildlife observation.
Robert Thatcher is a freelance publisher based in Cupertino, California. He publishes articles and reports in various ezines and provides night vision resources on [http://www.about-night-vision.info]