Binocular Definitions

Magnification
The enlargement of an object as viewed through a binocular. Higher magnification means less brightness, shorter depth of field, narrower field of view and harder to hold steady. Magnification represents the first number in the binocular description. i.e. a 7×50 binocular has a magnification of 7x. Steiner has objective lenses available in 6x, 7x, 8x, 8.5x, 10x, 10.5x, 12x, 15x and 20x.

Objective Lens (Width)
The diameter of the front lens, measured in millimeters. The objective lens produces the image, creates the initial focal point, inverts the image and creates the exit pupil. By doubling the objective size, it quadruples the brightness and doubles its ability to resolve images sharply. Objective lens represents the second number in the binocular description. i.e. a 7×50 binocular has an objective lens of 50mm. Steiner’s objective lenses range from 22mm to 80mm.

Field of View (F.O.V.)
The width of the area you see from left to right when looking through the binoculars. Field of view is generally expressed at a distance of 1,000 yards.

Coated
One surface of one or more lenses has received a coating.

Fully Coated
All lens surfaces are coated.

Multi-coated
One or more surfaces are multi-layer coated.

Fully Multi Coated
All lens surfaces are multi-layer coated.

Center Focus
Center focus allows the user to get closer to the object they are viewing. These binoculars are adjusted by focusing the center wheel.

Auto-Focus/Individual Focus (IF)
Once focus is set by setting each diopter to your eyes, images will always be sharp from 20 yards to infinity and no further adjustment will be needed. There is no focus wheel on Auto-focus binoculars.

Eye Relief
Eye relief is the distance from the eyepiece to your eye while still allowing the full field of view to be seen. Generally eyeglass and sunglass wearers need at least 15mm to 20mm of eye relief.

Exit Pupil
The exit pupil is the measurement of the size of the beam of light which is transmitted through the binocular and back to the eye. It is calculated by dividing the magnification into the objective lens diameter.

Twilight Factor
The amount of detail that can be seen in low light situations. It is calculated by taking the square root of the magnification times the objective lens.

Prisms Systems
Corrects the inverted and reversed image and allows the binocular to be shorter. There are two types of prisms – Roof (center fast focus) and Porro (sports auto focus).

Roof Prism
Features straight, streamlined barrels. High precision tolerances make premium quality roofs more expensive. Roof prisms are more compact and have a closer focus.

Porro Prism
Features offset barrels, wide field of view, and excellent image quality. Porro prisms are more rugged and have a wider field of view.

Diopter
The focus system that allows for the slight difference between the right and left eye of the user. Steiner’s diopter adjustment is on the left eye piece on roof prism only.

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~ by BinocularSpecialists on May 14, 2011.

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