Night Vision Glossary
How Night Vision Works
Night vision monoculars and binoculars work on methods of image intensification which means light amplification. Doing the best with the light from the image.
So it essential to understand that it is not the size of the objective lens which makes an image, it is what the monocular or binocular can do with the little light if no light at all which enters it.
You can use a night vision monocular or binocular in a room at home with the lights switched off at night and see you all the furniture but none of it is magnified.
So the canary on its perch will look like the dark picture without a monocular or binocular and like the lighter picture with one. Night-vision devices rely on a special tube, called an image-intensifier tube, to collect and amplify infrared and visible light. They need energy to work which comes from a simple battery.
In night vision systems, the objective lens collects light that you cannot see with your naked eye and focuses it on the image intensifier.
Inside the image intensifier a photo-cathode absorbs this light energy and converts it into electrons. When this highly intensified electron image strikes the phosphor screen, it causes the screen to emit light that you can see.
Since the phosphor screen emits this light in exactly the same pattern and degrees of intensity as the light that is collected by the objective lens, the bright night-time image you see in the eyepiece corresponds precisely to the outside scene you are viewing.
Night Vision phosphor screen is purposefully colored green because the human eye can differentiate more shades of green than other phosphor colors.
From then on you are in the world of how can manufacturers of night vision devices make the image better for you. Bigger, lighter, how far away the image has to be before you can see it e.g. 10 yards or a 1000 yards.
It depends what you need and you don?t have to spend a fortune on a Generation 2 scope when you only needed a Generation 1 scope.
The whole range of Foresight Optical Night vision devices have been chosen to offer the best qualities for whatever image you are looking at and whenever. We have something to suit you needs.
The main difference between various night vision devices is the intensifier or photo-cathode tube.
These type of devices usually have medium gain values giving good images. These intensifiers are comprised of simple electrostatic tubes. Light reflected from the subject strikes a multi-alkali coated photo-cathode, which produces electrons where the light strikes it. These electrons are displayed on the phosphor screen which in turn provides an image that is magnified and easily viewed by the scope?s eyepiece. Nearly always cheaper and often larger they give the best value for money for all uses. They intensify the light at approximately 500-20,000 times
They are generally smaller in size and weight and use noticeably less current. They were improved through the development of the micro-channel plate which intensifies the light at approximately 20,00-75,000 times.
This group is the most sophisticated technology available. The photo-cathode is coated with sensitive gallium arsenide which allows for a more efficient conversion of light to electrical energy at extremely low levels of light. The treatment makes the finished article three times more sensitive and also three times more expensive. The very high cost of this device and regulations for buying one mean that the man-in-the-street cannot get one.
The effective viewing range of the night vision device varies from 10 to 600m. The maximum viewing distance depends on the environment conditions. Dark conditions, fog, rain, twilight etc. may reduce the effective distance. An infra-red illuminator will increase your viewing range.
Night vision device needs some light to work so it is possible to see a bright image in low light or no light conditions with the use of an infra-red illuminator, which can be either built-in or attached to the device. The infra-red illuminator is either standard, or as an option and has a maximum effective distance between 75 and 250 ft. Avoid strong direct light, even sunlight or car headlamps, strong flashlights etc. as they may be harmful to your night vision device it if you direct you device at the source of these intense lights.
Night vision products comply with safety regulations in terms of safety and work on the same principles as televisions so there is no known danger, however if your eyes get tired watching television, you may experience the same sort of fatigue using your device for a long time.