Porro Prisms
The "classical" prisms: binoculars with porro prisms are, as a rule, wider than comparable roof prism binoculars, but not as long. Owing to the fact that the lenses are further apart, conventional porro prism binoculars offer a slightly more 3D image at short distances.
Roof Prisms
These are very compact and thus lead to particularly slim binoculars. A higher level of precision engineering is required for roof prism binoculars than for porro prism binoculars of the same quality level.
Bk-7 Prisms
Boron crown glass prisms, the standard for a quality image.
BaK-4 Prisms
Selected and carefully machined high performance prisms of barium crown glass provide even better resolution of detail and a brighter image with high colour fidelity.
Magnification
This value gives the apparent magnification of a lens. 8x magnification means that an object at a distance of 800 m appears to be at a distance of 100 m.
Lens
The lens diameter is given in mm. An important performance criterion for binoculars. The bigger it is, the more light it gathers and the brighter the field of view.
Exit Pupil / Brightness index / Twilight Factor
These are index values that result from the ratio of magnification and lens diameter. The following is important for real life: 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
This value specifies the width of the terrain that you can see 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. Binoculars marked Ww ( = wide angle ) have a particularly large field of view.
Minimum Focus
This number gives the shortest distance at which objects can be seen sharply and without distortion. This is important to know for use in museums, during tourist excursions or similar events.
Phase Correction
A particularly difficult surface treatment for prisms with special coatings. The ultimate for excellent image quality.
Internal focusing
Focusing means adjusting the "sharpness" of an image. Only the lenses inside the binoculars are moved during internal focusing. This means a closed system, which avoids sucking in dust, air and humidity.
All-Weather / Waterproof
Due to a system of water repellent features on the casing and the movable components, the binoculars are resistant to pressurized water.
Nitrogen Filled
Eschenbach binoculars for heavy duty, all-weather applications are filled with nitrogen (N2). This prevents misting up of the internal optical components in case of temperature changes.
Anti-Reflection Coating
Eschenbach binoculars have fully coated optics. This means that all air / lens interfaces are provided with an extremely thin anti-reflection coating to optimize the "light movement" through the binoculars to the eye. Coatings with magnesium fluoride are obviously standard; these are also known as blue coating. On some binoculars, this is combined with multi-coating on one side of the lens and the eyepiece to provide a "combi-coating" for even better light transmission. For the highest vision requirements, multi-coating is always used on all lens faces.
