Also commonly referred to as "power", magnification is a measure of how much closer an object appears when viewed through the instrument. For example, a 10x binocular will make an object appear 10-times closer than it would normally appear. An object positioned 100 yards away would appear as if it was just 10 yards away in a binocular with 10x magnification. The human eye is considered 1x magnification.

The edge-to-edge angular diameter of the image displayed in a binocular as seen by the eyes of the observer. It is an inherent specification for a given binocular design. The "angular diameter" of an object is defined as the angle an object makes (subtends) as seen by an observer.

The diameter of the circle of light exiting the binocular. Exit pupil is calculated by dividing the objective lens diameter by the binocular magnification. For example, a 10x50 binoculars has an exit pupil of 5mm (50/10=5). Knowing the exit pupil of a binocular can help determine the optimal binocular fro your needs. If a binocular exit pupil is larger than the dilation of the user's pupil, resolution is reduced since the maximum amount of light is not entering the eye. Typically under true dark adaptation a healthy human eye will dilate to approximately 7mm. This number can decrease with age and health factors.

Porro Prisms:

A binocular prism system that contains two right-angle prisms in each barrel offset from one another, requiring that the objective lenses be spaced further apart than the eyepieces. Optically, porro prisms often perform better than their roof prism counterparts.

Roof Prisms:

A compact binocular prism system that allows the objective lenses to line up directly with the eyepieces and hence yields a more portable binocular. Roof prism binoculars lose slightly more light to reflections than porro prism binoculars. High-quality roof prism binoculars compensate for this with special optical coatings.