Night vision is possible through some interesting techniques. In short, night vision devices work by increasing either the spectral range or intensity range at which human eyes can already see. Whether they maximize existing light or offer infrared illumination, night vision binoculars are a worthwhile investment for night-time surveillance, hunting, or use in the military. Learn all the ins and outs of how they work, how the different types are described, and how far they've come since World War II.
Night vision devices first appeared during World War II, and gained widespread use during the Vietnam war. They can be mounted on a helmet or on vehicles to give soldiers that extra edge while moving at night, and use various technologies to make sight possible in the darkest environments.
Night vision requires a greater spectral range or intensity range than needed for everyday bright sight. Some animals can see better in the dark than humans either because they can detect light closer to the ultraviolet or infrared range, or because their eye anatomy lets them see when light is less intense.
Night vision devices such as scopes, binoculars, and goggles, all use one or more methods to increase intensity range and/or spectral range. Typically any unit is built on an image intensification tube that maximizes available ambient light, whereas some also use infrared light.
During the Second World War, the first night binoculars could only work by increasing light intensity range. By having an objective lens diameter of 56mm or higher, they allowed as much light as possible through the binoculars. They also used a very large exit pupil – so large in fact that it was too big to be used by normal human pupils, and soldiers were issued eyedrops to compensate. However, these resulted in a very large, heavy set of binoculars that could be difficult to maneuver easily.
SOME INITIAL CONSIDERATIONS
These days night vision equipment can also increase spectral range by using infrared lighting. Although active infrared lighting is not appropriate for use in the military, since it can easily be detected by others with night vision goggles, it is useful in surveillance cameras. Some night vision equipment can be switched back and forth between active infrared lighting and passive magnification of existing light so you can choose the mode appropriate to your needs.
Typically night vision equipment is described using a “Generation” which refers to the technology used, from the Generation 0 sniper scopes used in World War II through to Generation IV devices. They can be found asmonoculars or binoculars, with various magnifications, and in different mounting options. You can find hand-held portable night vision scopes, rifle mounted scopes, or night vision goggles to be worn on the head.
Battery usage can be pretty heavy with night vision equipment that uses infrared illumination. If possible, look for a set that allow you to turn the infrared lighting off and on as needed, so you can avoid draining the batteries where possible. People often find night vision devices only work with freshly charged batteries as well. Still, you may find it is worth the investment to keep a charger and several spare batteries on hand.
On the other hand, some night vision sets have proximity sensors. These can be used to only activate infrared illumination when the device is in viewing position.
CHOOSING A SET
There is a wide range of night vision equipment available, and your first concern should be how a particular device can be mounted or used. For in-hand use, the ergonomics of the shell along with the weight of the unit can be most important.
Rifle scopes on the other hand need to be slim and streamlined as well as being durable and rugged. Night vision goggles may be preferable if you want your night vision equipment to always be available and hands free.
Bushnell offers a unique feature with their 2.5x42 Night Vision Monocular - a high-sensitivity microphone and earphones so you can detect sound up to 90 yards away. Although nicely designed for in-hand use, this unit also comes with a tripod mount. It includes a built-in infrared illuminator, takes only 2 AA batteries, and weighs in at just over one pound.
Fujinon offers a super compact night vision monocular that weighs only 13oz and is ergonomically designed to be comfortable and lightweight. Yet it's nearly indestructible, made of aircraft aluminum, and includes a built-in infrared illuminator as well.
Field of view and depth perception vary from unit to unit, and while there are inexpensive goggles for kids, there are also high end scopes for hunting and camping. If possible look for reviews or talk to people who have actually used the set you are considering to see how they hold up and how well they work. When it comes to night vision, image clarity is so subjective that you really need to try the device to see how well it works for you.