Scout Master

Night vision equipment work in the near-infrared band at a wavelength of about 1 micrometer. Unlike thermal imaging systems, which operate in complete darkness by detecting heat radiation signatures in infrared wavelengths beyond 3 micrometers, night vision works in near darkness by detecting ordinary ambient light, usually from the moon and stars, that is reflected by objects in the scene being viewed. Night vision contains an image intensifier tube that uses the photoelectric effect to amplify very weak light. As each photon of incoming light collides with a detector plate inside the intensifier tube, the plate ejects several electrons that are further amplified into a cascade of electrons. These electrons are accelerated by a strong electric field towards a phosphor screen which emits light at the point of impact of the electrons. A bright image is thus formed on the phosphor screen. Outdoor environments that are illuminated only by star light can be easily viewed using night vision devices.

Most night vision devices do not detect color information, and hence a monochromatic phosphor screen is sufficient. A green phosphor display is generally used because the human eye is most sensitive to the color green, which falls in the middle of the visible light spectrum.

Binoculars have a long history of military use. Galilean designs were widely used up to the end of the 19th century when they gave way to porro prism types. Binoculars constructed for general military use tend to be more heavily ruggedized than their civilian counterparts. They generally avoid more fragile center focus arrangements in favor of independent focus. Prism sets in military binoculars may have redundant aluminized coatings on their prism sets to guarantee they don’t lose their reflective qualities if they get wet. Military binoculars of the cold war era were sometimes fitted with passive sensors that detected active IR emissions, while modern ones usually are fitted with filters blocking laser beams. Further, binoculars designed for military usage may include a stadiametric reticle in one ocular in order to facilitate range estimation.

There are binoculars designed specifically for civilian and military use at sea. Hand held models will be 5× to 7× but with very large prism sets combined with eyepieces designed to give generous eye relief. This optical combination prevents the image vignetting or going dark when the binocular is pitching and vibrating relative to the viewer’s eye. Large, high-magnification models with large objectives are also used in fixed mountings.

Very large binocular naval rangefinders have been used, although late-20th century technology made this application redundant.