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Buyer's Guide to Binoculars

There are many considerations in choosing a binocular. Magnification and size are important, but quality and clarity are more important.

Unhappy with your current binoculars? You probably don't need more magnification, but rather greater brightness and/or better resolution from higher quality optical coatings. In other words, not all 8 power binoculars are created equally! Keep reading below.

Numbering System

Binoculars usually have several numbers printed on them, for example "7x42," "Field 7°," "367 feet @ 1000 yards," etc.

  • The "7x" means a magnification of 7 times.
  • The "42" means a front lens diameter on each barrel of 42mm wide.
  • The "Field 7°" means the size, from side to side, of the area that can be seen while looking through the binocular. That Field of View width can also be expressed as "367 feet wide at 1000 yards" in front of you.

Size (Front Lens Diameter)

The diameter of the front (objective) lenses determines the overall size of the binocular. Compact binoculars have 20-28mm front lens diameters, medium size binoculars have 30-42mm front lens diameters, and full size binoculars have lens diameters of 42mm and greater.

The diameter of the lens determines the light gathering ability of the instrument. Larger lenses let more light into the binocular so you see in greater detail. Larger lenses are important when viewing in low light or in the woods. The absolute brightness of the binocular is a calculation called Exit Pupil (see below).

Magnification (Power)

Power (magnification) is the degree to which the object being viewed is enlarged. Most binoculars magnify 7x, 8x, or 10x. A 7x binocular magnifies an image 7 times larger than it can be seen with the naked eye. The power affects the brightness and the field of view of the image. Generally, lower power is brighter and has a wider field of view than higher power.

Example of Increasing Magnification

Is higher power always better? No! Following moving targets such as birds in flight or footballs in play may be more difficult at higher (10x and more) powers because you have a narrower field of view. It may be difficult to keep the bird or ball in view.

10 power and higher may be hard to hold steady, therefore the images seem blurry or jumpy. The higher the power, the more the instrument magnifies our body movement from heartbeat, breathing or caffeine! More than half of our customers find a 10x binocular too difficult to hold steadily. Some manufacturers make binoculars higher than 10x and they can be very hard to hold still. Tripod adapters are usually available for these high power models.

Higher power binoculars may seem less clear if you are viewing on a hazy day. Heat waves, moisture, dust, or fog will be more visible when viewing through 10x binoculars rather than 7x or 8x models. Remember, binoculars (and telescopes) magnify not just your ultimate target but any particles in the air between you and that target!

Field of View

Field of View Explanation

The size of the area that can be seen while looking through binoculars is referred to as the field of view. The angular field is indicated, in degrees, on the outside of the binocular. The linear field refers to the area that can be observed at 1,000 feet in front of you. A larger field of view means a wider or larger viewing area.

Field of view is related to magnification. Lower power has a wider field of view. Higher power has a narrower field of view. A wide field is desirable when viewing moving objects or when the binocular user may be moving (i.e. on a boat).

Multiply the angular field by 52.5' to determine the linear field. A 7-degree angular field has a 367' linear field at 1,000 yards in front of you.

Exit Pupil (Brightness)

Exit pupil is an important consideration. The diameter of the beam of light that leaves the eyepiece and hits your pupil is the exit pupil. The larger the exit pupil, the brighter the image. Large exit pupils are desirable for low light viewing such as dawn, dusk, in the woods, or for binocular astronomy.

The human eye pupil diameter is about 2mm in bright light, 3-5mm during normal daylight, 5-7mm at dawn or dusk and 7+mm in total darkness. You have good viewing when the binocular exit pupil is greater than or equal to the diameter of your eye pupils. If the exit pupil is insufficient for the lighting conditions, you will see less detail. It is much like walking into a dimly lighted room vs. a fully lighted room – you see more detail in full light.

To calculate exit pupil, divide the size of the objective lens by the magnification of the binocular. The exit pupil of a 7x42 binocular is 42 divided by 7 = 6mm. The beam of light hitting each of your pupils is 6mm wide.

Consider the impact of magnification on exit pupil: 7x50 and 10x50 binoculars are both full size instruments. The exit pupil of a 7x50 is 7.1mm, whereas the exit pupil of the 10x50 is 5mm. The 7x50 will provide brighter images, yet less magnification.

Eye Relief

Eye relief is the distance, in millimeters, that a binocular can be held from the eye and the full field of view can still be seen. This is important for eyeglass wearers because they cannot hold the binocular as closely to the eye as someone without glasses. Eye relief of 14mm or more is desirable for eyeglass wearers.

Optical Coatings

The coatings on a binocular are very important to the quality of the image you see. All optical glass absorbs and reflects light; light transmission through poorly coated glass can be as low as 50%! This means that up to half the available light is not hitting your eyes!

The optical elements of the binocular are therefore coated to reduce light loss and glare. This ensures even light transmission, brightness, greater clarity, sharpness and contrast. Lens coating levels range in quality as follows: coated, fully coated, multicoated, and fully multicoated. Fully multicoated lenses are the best with as much as 95% light transmission. Terminology may vary from one manufacturer to another; some multicoated lenses may in fact be fully multicoated. We can help you understand any noticeable differences.


Types of Prisms

There are two basic designs: roof or porro. By design, straight tube roof prisms are more compact, yet are more difficult to properly make. The incoming light is reflected five times in a roof prism prior to hitting your eye, meaning an inherent loss of light as compared to four times in a porro prism.

High quality roof prisms overcome this light loss with special reflective coatings to amplify the brightness. Inexpensive roof prisms will look dim compared to the same size porro prism model.

Porro prisms are designated either BK-7 or BAK-4. We would recommend that you do not buy a binocular with a BAK-7 prism system. BAK-4 prisms are denser and of better quality. To see the type of porro prism, hold the binoculars at arm's length and look in to the oculars. If you see 2 perfectly round circles, these are BAK-4 porro prisms. If the two beams of light are more diamond-shaped, these are the less expensive BK-7 porro prisms.

Porro prism binoculars have a more traditional appearance than roof prism binoculars. Medium and full-size Porro prism models often have better depth of field than roof prism binoculars because the prisms are farther apart. Better depth of field means you will have more of the foreground and background in focus at the same time.

Roof vs. Porro Prisms
Light flow through roof vs. porro prism binoculars

Near Focus

The distance between the binocular and the nearest object you can focus on, while maintaining a sharp focus is the near focus. Lower power generally has a closer focus than higher power instruments. There are some binoculars on the market with very close focusing ability, such as the Papilio series from Pentax with an 18-inch close focus! See butterflies with that model (or your shoe laces)!


The alignment of the optical elements of the binocular is the collimation. Good collimation prevents headaches and eyestrain. Very inexpensive binoculars usually have poor collimation. If you see a double image when viewing through a binocular, it may be "out of collimation".

If the binocular has been dropped, it may need to be collimated by the manufacturer. You cannot collimate a binocular yourself - quality manufacturers use laser collimation devices to ensure precise alignment.

Interpupilary Distance

When looking through a binocular, you need to adjust the two barrels around the center hinge(s) so that you see ONE image, not two images. That means the binocular oculars are properly centered on your pupils.

If you have close-set or wide-set eyes, not all binoculars will fit you. Roof prism designs have the closest possible interpupilary distance. Contact Out of This World for advice if you have eyes that are rather close together (or far apart).

Fit and Feel

There is a subjective aspect to choosing binoculars that cannot be denied! Some binoculars will feel better in your hands or fit your face better than others. Size and weight are factors, as are balance and quality. The staff at Out of This World has years of experience and will be happy to help you make your decision!

Waterproof vs. Water Resistant

There is a vast difference between waterproof and water-resistant (or weather resistant). Waterproof means the binocular has been purged of all moisture and air then filled with an inert gas and sealed with O-rings. Waterproof binoculars are fog proof and will suffer no internal condensation if immersed accidentally in water for brief periods of time.

"Water resistant" is typically a marketing expression that means the construction has very little protection against moisture. There are, however, some very good quality water-resistant models that will afford you good moisture protection because of their superior construction.

It is a common misconception that binoculars housed in rubber are waterproof. Rubber casing is for grip only and is not a determinant of waterproofing.

Zoom Binoculars

There are many zoom binoculars on the market with changeable magnification. A typical zoom will have powers of 7-20x. Beware of zoom binoculars! Most zooms are of bad optical quality and resolution. Most zooms feature magnifications too high for comfortable handholding (remember most of us find 10x to be the highest power we can hold without shaking too much). And, don't forget to calculate the exit pupil and field of view on zooms -most have dim, fuzzy images with very narrow fields of view.

There are a few good quality zoom binoculars on the market and Out of This World sells them. The ones we don't sell - well, we highly recommend against buying them! They just don't provide acceptable image quality.

Fixed-Focus or Auto-Focus Binoculars

There are some binoculars sold which claim to have a fixed or automatic focus. These are units with the focus factory preset at infinity and will be somewhat in focus from about 40 feet (at 7x) or 80 feet (at 10x) to infinity. You cannot obtain a truly sharp focus and you cannot compensate for a left and right eye vision imbalance with the diopter control available on standard binoculars.

We do not recommend fixed or auto focus binoculars. They are a marketing gimmick and provide fuzzy images when compared to a focusing instrument. They feature low-grade prisms and coatings. A quality porro prism binocular has a wide depth of field that will require little focusing once set for your eyes.

Are $1,500 Binoculars 15 times better than $100 Binoculars?

Maybe! Top of the line binoculars can be clearer, sharper and brighter than comparably sized models at a lower price. But in recent years, medium-priced binoculars have improved considerably in quality and features.

Do you need the very best? The staff at Out of This World will help you find the right model for your budget. Many very fine binoculars are available in all price ranges; we specialize in finding the best binocular for you!

Out of This World is an Authorized Dealer for the following optic brands: