Binocular Buying Guide

Binoculars

Binoculars, (also known as Field glasses) are optical devices that contain dual mirror-symmetrical telescopes mounted together in order for the user to use both eyes when viewing distant objects. Binocular lenses are aligned to point accurately in the same direction, many binoculars are designed to be held by two hands but there are much larger models as well. Binoculars give the user a three dimensional view; the two views contain a slightly different viewpoint to each of the viewer's eye, thus producing a merged view with depth perception. there are two types of binoculars that are used today; Roof Binoculars and Porro Binoculars. you will find many different sizes and styles of binoculars. The most important thing to look for in a set of binoculars is that; it should feel good in your hands and be able to get a clear/crisp image.

Types of Binoculars

Roof Binoculars

Roof Binoculars contain what is known as a roof prism, these binocular models are generally smaller in size than porro style binoculars and are typified by straight barrels. Roof prism models are lighter weight than porro prism binoculars yet maintain excellent image quality. Roof prisms usually have a more sleek design than parro prisms but have a reduced brightness compared to the parro. These binoculars must go through a more strict alignment of the optical elements which requires the elements to be a fixed style. This means that they normally do not need to be re-aligned.

Parro Binoculars

Porro Binoculars contain what is known as a parro prism, these models are a more traditional style binocular. Porro prism binoculars are easily identified by the shape of the barrels, which have the objective lens offset from the ocular lens. Parro prisms produce a brighter image versus the roof prism, but the prisms may need to be re-aligned occasionally.

Binocular Sizes

Compact

Compact binoculars offer the advantages of being smaller and lighter. They are perfect for those who are generally on foot for long periods of time and need to trim weight from their load. They usually fit into pockets for easy accessibility and quick use. However, they offer limited light transmission and steadiness in the larger powers. Usually, objective lenses in these compacts are in the 20-30 mm range.

Mid Size

A Mid size binocular offers a good mix of light transmission and steadiness, but is also easy to handle and fairly lightweight is a mid size. These binoculars are great for all around use in most conditions. Objective sizes in mid size binoculars typically range from 30-40 mm. These days, many features of full size binoculars can be found in mid size binoculars, a plus when weight is critical.

Full Size

Full size binoculars are the best for gathering light because of their larger objective lenses, which are usually over 40 mm. They also offer broader fields of view and are easier to steady. The trade off is often in the size and weight. Larger and heavier, they are ideal for those who don’t mind carrying a few extra ounces to get a better view.

Power and Viewing

Power and Objective Size, Zoom Options

Optics are described by two numbers separated by an “X.” The first number is the magnification (8X) or how many times larger an object will appear when viewed through the optic. An 8X, or 8 power optic will make an object appear eight times closer than the same object viewed with the naked eye. The last number is the diameter of the objective lens in millimeters (X40). The objective lens is the lens nearest the object being viewed. When choosing a binocular, magnification is critical. Lower magnification binoculars, 8X or less, allow for excellent light gathering, wider field of view and extremely steady images. Higher magnification binoculars, 10X or higher, bring objects much closer, but sacrifice some of the other features found in low magnification pairs.

Field of View (FOV)

When viewing through a binocular the visible width at a given distance is known as the “field of view.” Field of view may be expressed in feet at 1,000 yards, meters at 1,000 meters, or degree of angle. One degree of angle equals 52.5 feet field-of view at 1,000 yards. An optic with 6.5 degrees of angle can be calculated by multiplying 52.5 feet (6.5 x 52.5 = 340 feet at 1,000 yards). TIP: Higher magnification means closer images but less light transmission and smaller field of view.

Inside the Optic

Lens Construction

Another more recent innovation in binocular lenses is the attention to ocular lens configuration. The arrangement and surface shape can effect clarity and definition, especially at the edges of the image. Brunton Epoch™ binoculars use “hybrid aspheric lens construction,” a complex organization of lens surfaces that result in optimal image clarity over the entire image field and eliminate distortion found in standard aspheric lenses.

Coatings

To enhance light transmission through a binocular, manufacturers apply a microscopic film containing magnesium fluoride and other chemicals to the prism, lenses or both. This microscopic film diminishes the reflected or stray light inside a binocular allowing more light to be transmitted to the user’s eye. Generally, the more applications of this coating, the greater the reduction in glare and reflections resulting in a brighter crisper image. The least expensive process is known as a “coated” optic where only the prism is coated. When an optic is “fully coated,” all air-to-glass surfaces (lens and prisms) are coated once. The best coating available is “fully multi coated” where all air-to-glass surfaces are coated multiple times for the greatest amount of light transmission to the eye. TIP: More coatings mean brighter, crisper images in all light conditions. Exit Pupil & Eye Relief.

Exit pupil

The amount of light exiting the binocular and entering the eye is determined by the “exit pupil.” The exit pupil is calculated by dividing the diameter of the objective lens by the magnification. An 8x40 mm binocular has an exit pupil of 5mm (40 mm ÷ 8 mm = 5 mm). If we were glassing for elk during the day, the pupil of a human eye would only open 2.5 mm, but increase to 5 mm at dusk to compensate for less available light. Binoculars with an exit pupil of 5 mm or higher maximize the amount of light entering the eye, thus increasing image brightness. An 8X24 mm binocular (3 mm exit pupil) will perform well under normal lighting conditions where a 7X42 mm binocular (6 mm exit pupil) provides enough light to see during twilight conditions and into the shadows of the forest canopy.

Eye Relief

In order for your binocular to produce a full image, the proper distance must be maintained from your eye to the ocular lens. This distance is known as “eye relief.” If you wear eyeglasses (or sunglasses), the distance is increased because your eyes are 10-15 mm behind a glass barrier. If this additional distance is not accounted for “tunnel vision” will occur. To allow eyeglass wearers to have a full image, a binocular must incorporate “long eye relief” which is a distance of 15 mm or more. Binoculars with long eye relief feature adjustable eyecups which move the binocular to the correct distance from the eye for eyeglass compatibility. Recent innovations such as “multi-step long eye relief” allow the user to twist-up the eyecups to the desired distance from the eye. Brunton Epoch™ Binoculars feature a patented “locking multi-step eye relief system” which allows users to lock the eye cups in their specific position to ensure quicker spotting with less set-up of the binocular. TIP: Eyeglass wearers should seek a binocular with a minimum eye relief of 18 mm.

Focus Mechanisms

Focus settings

Focus mechanisms are critical to the performance and enjoyment of your binocular. A good focus wheel set-up will give you a range of closefocus to infinity in just one full turn (360 degrees) of the focus wheel. Most binoculars have a linear focusing gear, which typically gives the user either a slow focus or fast focus. Slow focus is good for examining things at close range (less than 30 feet). Fast focus is better for long range viewing (30 ft to infinity). Brunton’s Variable Speed Focus™ allows the user a combination of fast and slow focus. Brunton has also set the bar for close focus. Typically, binoculars can not focus on objects closer than 5 ft away. The Epoch™ binoculars are able to focus at a mere 3 feet away, with precise focus adjustment, then transition out to infinity with a fast focusing gear. This innovative system has forever changed binocular performance standards.