Night Vision Binoculars
They Had Their Start in World War 11
When we think of night vision aids, we usually have two words that pop into our minds...military and infrared. Actually, it is very legitimate that the military is one of first things we think of because it was the military that first used night vision devices. World War 11 saw them initiated and they were later used during the Vietnam War. They could be mounted on a soldier's helmet or onto vehicles to give soldiers an edge in the dark.
The obvious purpose of night vision binoculars, scopes, and goggles is to be able to distinguish activity in the dark. Unlike daylight vision, night vision apparatus needs more intensity range and they all use one or more methods to increase intensity range. This can be done through the maximization of available ambient light or by using infrared light. During WW11, the first night binoculars only worked by increasing light intensity range. The excessively large objective lens diameter of 56mm or more, allowed as much light as possible through the binoculars, but the large exit pupil that had to be used made the binoculars almost impossible for the human eye to adjust to - soldiers had to use eye drops to live with these units. Additionally, they were unbelievably heavy and difficult to maneuver.
Passive and Active Technology
Night vision binoculars work in one of two ways - either passively through the lenses or actively using a thermal or infrared image. The early models used passive technology, however, the modern versions use active technology because it is more state-of-the-art and sophisticated. Infrared lighting is not used in a military setting because it gives away location. However, it is useful for surveillance cameras and equipment and some night vision equipment can be switched back and forth between active infrared lighting and passive magnification of existing light so it can be manipulated by hand if necessary.
In a passive system, like the one used by the military in the Second World War, the night vision binoculars have a very wide lens opening which is designed to collect as much light as possible. The light passes through a series of intensifying filters before being emitted through a very small aperture, allowing the wearer to see in the dark. The tint of this type of lens is green. It is usually left that way rather than trying to change it because correcting the green tone could obscure the image.
Sophisticated Active Night Vision Binoculars
Sophisticated active night vision binoculars are capable of providing a sharp and clear picture. The less complicated thermal imaging versions just display blotches of color and indicate bright spots where an animal or engine may be present. Active systems "see" through smoke, fog, dust, and other visual cloudiness whereas passive systems cannot.
Although we associate infrared or night vision with the military and police surveillance, it is also very useful for the hunter who wants to observe animals in their habitat. Hand-held portable night vision scopes, rifle mounted scopes, night vision goggles and night vision binoculars are popular with hunters who want to be in the woods in the very early morning or at dusk, when animals are on the move.