Binocular Terminology You Should Know
Coated Optics:
The coatings on a lens surface which reduces light loss glare due to reflection, which results in a brighter, higher-contrast image and reduces eye strain.
Coatings:
Coated: single layer on at least one lens
Fully-coated: A single layer of all air-to-glass surfaces
Multi-coated: multiple layers on at least one lens and all surfaces at least once
Fully Multi-coated: Multiple layers on all air-to-glass surfaces.
Exit Pupil:
Exit pupil refers to the size of the column of light that exits an eyepiece. The larger the exit pupil, the brighter the image. To determine the size, divide the objective lens diameter by the magnification. E.g. a 12 x 36mm binocular has an exit pupil of 3mm.
Eye Relief:
The distance an eyepiece can be held away from your eye and still provide a full field of vision. If you wear glasses, you should look for
extended or long eye relief.
Field of View:
This is the side-to-side measurement of the circular viewing field. It’s defined by the width in feet (or meters) of the visible area at 1,000 yards. A wide field of view is preferable for following fast-moving action or wildlife. The higher the magnification = a narrower field of view.
Magnification or Power:
Binoculars and scopes are referred to by two numbers, with an “x” in the middle, such as 12 x 36mm. The “12″ is the magnification of the lens, which means the object will appear 12 times closer than you will see it with just your eyes.
Objective Lens Size:
The second number in the 12 x 36mm (36mm)refers to the diameter of the front lens in millimeters. The larger the front lens (aka objective lens), the brighter the image because more light is passing through.
Prism Glass:
Most optical prisms are made from either borosilicate (BK-7) or barium crown (BAK-4) glass. BAK-4 is a higher quality glass which
yields brighter images and sharper edges.
Prism Systems:
Without a prism system, you would see your images upside down when looking through your binoculars or scope.
Waterproofing/Fog-proofing:
Some binoculars/scopes are sealed with o-rings and nitrogen purged for protection, allowing them to withstand total immersion while remaining dry inside.