...your guide to using optics.

Binocular Terms: (G - N)

Individual Focus Binoculars

Each eyepiece of the binocular focuses independently of the other (unlike with a center focus binocular which adjusts both eyepieces at the same time).

Light-Gathering Power

The light-gathering power of a binocular is determined by the surface area of its objective lens.

Light Transmission

Light transmission describes the percentage of available light passing through a binocular to the viewer's eye. Better coatings on the optics of a binocular increase the amount of light that reaches the eye.


Higher magnification allows you to see more detail through the binocular.

Note: As the magnification of a binocular increases, the field of view decreases.

Multi-Coated Optics

Binoculars with multi-coated optics have one or more surfaces coated.

Note: Within a binocular the coatings may vary from one surface to another. For example, one surface may not have any coatings, another may have only one coating, while another may have several coatings.

Nitrogen Purged

The atmospheric air within the binocular is replaced with nitrogen. This prevents mold, mildew or acid etching of binocular lenses and prisms that atmospheric air (containing moisture) would permit. Most waterproof binoculars are nitrogen purged.
Note: Temperature changes, elevation changes, or extreme humidity can create internal fogging. Most of the time this moisture dissipates on its own in a matter of minutes.

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