Night Vision Basics
The human eye enables comfortable vision from dawn to dusk but its performance becomes limited as darkness falls. Thus, a technology that allows operations during night-time gives a tactical advantage over the adversary. Today, most operations are planned and executed during the night.
A technology that provides full capability during night-time operations, such as walking, reading, navigating, driving, fighting etc., is image intensification. Image intensifier tubes integrated in various instruments such as monoculars, binoculars, sights, clip-ons, periscopes etc. enable night-time observation and aiming in nights with illumination down to overcast starlight (moonless).
Image intensifier tubes operate using an electro-optical conversion. In a typical instrument, light (photons) from the observed scene is focused by the objective lens on the photocathode and it is converted to electrons. Subsequently, the electrons are multiplied using a high-voltage micro-channel plate. Finally, the electrons impact on a phosphor screen next to the microchannel plate and are converted back into photos for the eye to see by means of an eyepiece. The phosphor used is usually green, giving the characteristic well known colour to the image of intensified systems. Two broad types of image intensifier tubes are available; Gen2 and Gen3. The major difference is the material of the photocathode. Both can give top-grade performance.
The image intensifier tube’s most important characteristics are resolution and signal-to-noise ratio (SNR). Resolution is indicative of the finest details that can be imaged, while SNR dictates the performance at low light levels. AUTOGATING is an important feature that enables dynamic response to changing light conditions, such as explosions or entering bright rooms and gives a tactical advantage.