Night binoculars are available in a wide variety of focal and light intensities.
Night binoculars were designed to increase the visibility of objects in the dark. Night binoculars are just one product among a number of military, professional and commercial night vision devices (NVDs) in use by military personnel, police, intelligence services and even hunters and hobbyists. Night binoculars amplify visible light and form images from radiation wavelengths the human eye can't detect.
Both the United States and its allies and the Germans developed early night vision technologies during World War II, including infrared sniper scopes and night binoculars issued to allied forces during the Sicilian invasion. The devices were designed to use available light to the fullest extent possible in low-light conditions. Since then the technology has expanded to use by forensic scientists, manuscript researchers and restorers and even surveillance systems.
NVDs are designed to emulate night vision, or the ability to see objects in poor light. Night vision is correlated to the retinas rod cells whose molecules, known as rhodopsin, absorb light. This is why the eye has to adjust to sudden transitions from light to darkness. Animals actually have an additional tissue layer called the tapetum lucidum to reflect light back through the retina, thus they are far better than people at seeing in the dark
Night binoculars emulate night vision, but that doesnt mean the experience is the same as seeing objects in full daylight. Vision using night binoculars or other NVDs, even under optimal conditions, is 20/25 to 20/40 (20/20 is considered perfect), and that decreases as an objects contrast and illumination fade. Night binoculars make it more difficult to estimate an objects distance and depth and reduce the field of vision by as much as 40 percent.
Night binoculars amplify existing ambient light through an enlarged lens. This can be starlight, moonlight or even infrared light). Generally, these devices use two approaches: image intensification, translating light from the near-infrared spectrum onto patterns from the visible spectrum, and thermal imaging, which translates light from the infrared spectrum onto visible light. Image intensifiers require that some light be available, but can amplify the light by a degree of 2,000 to 5,000. On the other, hand, thermal devices, also called Thermal Forward-Looking Infrared (FLIR) sensors contrast the temperature between an object and its environment. Every device uses photons to knock electrons free and amplify their current to project visible light.
NASA refers to thermal imaging technology as thermography and suggests the applications range far beyond military, police and security uses. Basically binoculars use thermal imaging to detect objects and their features based on their heat signatures, which cant be detected by the human eye. The sensors are made from materials that detect radiation signals indicating temperature differences and show images in black and white, green or a variety of colors. Devices that use image intensification amplify light by forcing parallel light rays through thin disks of narrow glass cylinders and apply voltage to knock more electrons loose. Devices using image intensification are lighter and less expensive than thermal systems, but cant work in absolutely lightless conditions.
Although the technology was started back in WWII, it wasnt until the Vietnam War that NVDs were used by troops in the field. Devices incorporated thermal imaging technologies in the 1970s that would evolve into Forward Looking Infrared (FLIR) systems, which allowed visibility in a number of low-visibility situations in addition to nighttime, such as smoke or haze. By the 1990s, and the U.S. operations in Iraq, NVDs had become essential tools of warfare. Night vision technology is generally considered to break down into three generations, with the third generation being the most developed:
The applications for night binoculars and other NVDs seem limitless. FEMA suggests that night vision is useful in any number of surface and air applications including port security, responding to fires, search and rescue operations, counter-terrorism surveillance and even detecting and responding to intrusions (for example burglars or thieves can be detected moving around in a closed building). They say that handheld binoculars are particularly useful in rural environments where ambient lighting can be low.
Thermal imaging has also been brought into industrial applications including energy audits, process control and tracking down malfunctions in machines. Night binoculars can be used for environmental research, detecting oil or toxic spills and wildlife migration. Doctors use thermal imaging to detect abnormal temperature variations in the human body. Unusually high or low temperatures could indicate the need for medical attention.
Hunters and naturalists can use night binoculars to track wildlife. They can be particularly useful, not just at night, but in dense woods or foggy conditions. Models differ, including standard binocular as well as monocular. Special headgear is available that allows users to mount the binoculars and keep their hands free. Buyers should make sure a particular pair of binoculars is suited to the specific task, or range of tasks for which they are intended. Typical personal uses include:
Night binoculars can also be used for cave exploration, night-time fishing or boating and scouting games.