Binocular Terminology
From Bushnell

Optical performance relies on the successful balance of a number of factors. When each factor is optimized, the result is an instrument with outstanding visual performance.

Prism Systems Binoculars have left and right side barrels linked to each other by an axle. The two most frequently used prism systems are porro and roof.

Porro Prism binoculars are characterized by the eyepieces being offset from the objective lenses.

Roof Prism binoculars feature lenses positioned in line for a more compact design.

Magnification Magnification is simply the degree to which the object is enlarged. With a 7x35 binocular, for example, the object appears to be seven times closer than without the aid of a binocular. The number immediately following the "x" is the diameter in millimeters of the objective (front) lens. A 10x50 binocular, therefore, has a 10 times magnification with a 50mm objective lens.

Exit Pupil The exit pupil refers to the size of the shaft of light transmitted to the eye. The more light, the better the contrast. You can actually see the exit pupil by holding the eyepiece of the binocular approximately 12 inches from your eye. It is the bright circle of light in the center of the eyepiece. Exit pupil is expressed in millimeters and is normally derived by dividing the power into the objective lens diameter. A 7x35 binocular has an exit pupil of 5mm (35 ÷ 7). A 15 power telescope with a 60mm objective lens diameter has an exit pupil of 4mm.

Coated Optics All Bushnell optical glass surfaces are coated by magnesium fluoride to reduce light loss and glare due to reflection. All Bausch & Lomb binoculars are fully multi-coated to further enhance viewing and reduce eye strain. InstaVision binoculars have a special image enhancing, amber, high contrast coating.

PC-3 phase coating system - Dramatically improves resolution and contrast by correcting the light phase-shift interference in roof prism binoculars. Available on Bausch & Lomb® Elite® roof prism models.

Rubber Eyecups All Bausch & Lomb and Bushnell binoculars come with soft rubber or pop-up eyecups. When rolled or pushed down they permit eyeglass wearers to enjoy an improved field of view.

Field of View The field of view is the width, measured in degrees or feet, of the viewing area you would see at 1,000 yards.

Focus Systems Insta-Focus® - A touch of the fingertip is all it takes to hold your subject in sharp focus. This special focusing mechanism was developed and patented by Bushnell to let you follow the action and switch to another subject instantly.

Center Focus- One knob moves both lenses for fine focusing precision.

Individual Focus- This system is unique to the Bushnell standard sized marine binocular line. Well suited for people with large vision differences between left and right eyes.

Focus Free- Requires no focusing, the binoculars range is pre-set from 40 feet or 90 feet to infinity with your eyes doing the actual focusing.

 

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