The key technical terms are briefly explained here.
Porro prisms: The 'conventional' prisms. Binoculars with Porro prisms are normally wider than comparable roof prism binoculars, but not as long. Owing to their widerspaced objective lenses, conventional Porro binoculars offer slightly better stereoscopic depth perception at short distances than roof prism equivalents.
Roof prisms: These are very compact and therefore allow the binoculars to be built very slim in form. A higher level of optical precision engineering is required than for Porro binoculars of comparable quality.
BK-7 prisms: These prisms made from boron crown glass are the standard for a good quality image.
BaK-4 prisms: These carefully machined high performance prisms made from barium crown glass provide even better resolution of details and very sharp, bright images with high colour fidelity.
SK15 prisms: These prisms are made from high quality SK15 glass. They minimise unwanted internal reflections and provide razor-sharp images with optimum contrast.
Magnification: The value gives the apparent magnification that the lens produces. With an 8x magnification the object appears 8 times closer to the viewer than in reality . Here, an object appears to be only 100 m away when in fact it is at a distance of 800 m.
Lens diameter: This is an important performance figure of binoculars since its size crucially determines the lightgathering power: The bigger the lens, the more light that reaches the eye and the brighter the image. The objective lens diameter is stated in mm.
Exit pupil/Brightness index/Twilight factor: These are arithmetic values that result from the ratio of magnification and lens diameter. Important in practice: an exit pupil between 2 and 3 mm is sufficient for use in daylight. Binoculars with an exit pupil of 5-7 mm should be chosen for difficult light conditions.
Field of view: Specifies the width of terrain seen through the binoculars at a distance of 1,000 m. The greater the field of view, the easier it is to view landscapes or moving objects, such as animals or competitors at sports events. Binoculars with wide-angle optics (with the designation: Ww) have a particularly wide field of view.
Near point: This number indicates the shortest distance at which objects can be seen sharply and without distortion. This number is important when buying binoculars for use in museums or outings where viewing is at short range.
Phase correction: This particularly elaborate application of special surface coatings to the prisms of roof prism binoculars is the ultimate for outstanding image quality.
Dielectric mirror coating: A dielectric mirror coating inside the prism system allows almost 100% reflection of the incident light and prevents the coatings from ageing. This coating ensures contours always remain distinct and clearly discernible even in poor light conditions or during the twilight hours.
Internal focusing: Focusing means adjusting the sharpness of an image. Only the lenses inside the binoculars are moved during internal focusing. This closed system prevents dust, air or moisture from being drawn in.
Waterproof: This term refers to a system of water repellent features on the casing and moveable parts that makes the binoculars resistant to pressured water.
Nitrogen filled: In contrast to air, nitrogen contains no residual moisture and so prevents the internal optics from misting up if the ambient temperature fluctuates.
Coating: Eschenbach binoculars have fully multi-coated optics. This means that all glass-to-air surfaces have an extremely thin anti-reflection coating to optimise 'light movement' through the binoculars to the eyes. A magnesium fluoride coating (magenta coating) is the standard. On some binoculars this is combined with multi-coating on one side of the lens and eyepiece to improve light transmission. For the highest vision requirements though, multi-coating is applied to all lens surfaces.
To ensure true-to-life, completely colour accurate images, Eschenbach applies a 'naturebright' coating to its farlux, bison and regatta binoculars.
Extra-low-dispersion (ED) glass: This expensive to produce glass compensates for chromatic aberration that normally occurs due to the differing dispersion of the light-beam colour components and is seen as colour fringing along edges and at transitions. ED glass ensures vivid true colour images, extremely rich in detail and with a sense of depth.