How to Buy Binoculars

Buying Guides: How to Buy Binoculars

by: SportsmanGuys.com
This Binoculars Buying Guide will help you find binoculars based on the features listed below. This information will help you choose binoculars that are right for you!
Binocular magnification
How to Choose Binoculars by Magnification [Back to Top]

When choosing binoculars, Magnification is the first number (Example. 7x in the size 7x50 or 8x in the 8x40 binoculars)in the label. The definition of Magnification is simple, it's the measure of how many times (example 7x) the user can see an object through their binoculars than with their naked eye.

Look at the images to the right. The first picture labeled "Naked Eye" is the normal vision without binoculars. The pictures following are what the different sets of magnifications would look like when viewing through different binoculars. Notice the stronger the magnification is, the closer the object appears.

Choosing binocular magnification is not hard. Before buying binoculars, choose the binocular magnification number carefully. Remember, the larger the magnification doesn't always mean it's better. The higher the magnification goes,the brightness of the image and the field of view (how wide your view is) will decrease more and more. Also, as magnification increases, the binocular gets heavier which may make it harder to hold steady while using them. Most users stick with no more than a 10x binocular, this way they feel its controllable and don't need any additional support from a tripod.
Binocular objective lens diameter
How to Choose Binoculars by the Objective Lens Diameter [Back to Top]

The Objective Lens Diameter is the second number (Example. 50 in the size 7x50 or 40mm in the 8x40mm)in the label when choosing binoculars. The diameter is always measured in millimeters. Sometimes you will see the "mm" behind the number and sometimes not. The larger the objective lens, the more light that enters the binocular and the brighter the image.

Choosing binoculars with the wrong lens diameter can directly affect the performance of them. For example, the Zeiss Conquest 8x56 Binocular will produce a sharper and brighter image than the Zeiss Conquest 8x40 Binocular, even though they both have the same magnification of 8x. The Zeiss Conquest 8x56 will create wider beams of light that leave the eyepieces. Therefore, the higher the objective lens the brighter and sharper the image will appear. Considering this, most users prefer the 8x56 over the 8x40.

The downside of a larger front lens is the weight. Dependent upon the activity, the binoculars with a larger lens can be uncomfortable. If you're hiking for long hours, most users wouldn't want to carry such heavy binoculars around their neck. Therefore, choosing binoculars that are more compact in size such as an 8x25 would be better. Compact Binoculars are well rounded, allowing them to be used in a variety of activities such as sporting events, hunting, traveling, bird watching and more.
Binocular Exit Pupil
How to Choose Binoculars by the Exit Pupil [Back to Top]

The definition of Exit Pupil is the diameter of the beam of light that exits the eyepiece. It's calculated by dividing the objective lens diameter by the magnification. (Example. for an 8x42 binocular it would be 42mm/8x = 5.25)

In order to receive the full light gathering capability, the exit pupil must be equal to or greater than the diameter of the pupil at any given moment. During daytime hours, the size of a humans eye dialates from 2 to 3mm and during nighttime hours from 6 to 8mm. The larger the exit pupil is, the brighter the images will be in low light conditions. At SportsManGuys.com, our optics specialist recommend not going any higher than a 7 because the users eye cannot open that wide. The advantage of it being above 7 is its easier to hold steady and keep the center on the eye. This is why most marine binoculars are above 7.

When buying binoculars, choosing binoculars by the exit pupil, brightness and twilight factor should not be taken to serious since all binoculars are treated the same no matter the lens coating or optical quality.
How to Choose Binoculars by the Level of Brightness [Back to Top]

The Brightness level is the amount of light that enters the binoculars. The size of the exit pupil is what determines the brightness of the binoculars. The calculation of the brightness is simply the exit pupil squared. If the exit pupil is 3mm, then the level of brightness would be 9.

Before buying binoculars, consider if you'll be using them in low light conditions or in sunny weather. If you're using the binoculars in low light conditions, choose a higher exit pupil. If you're using the binoculars outdoors in the sunshine, choose a smaller one. Studies have shown premium compact binoculars with a low brightness level are actually brighter than some full size binoculars.

When buying binoculars, choosing binoculars by the exit pupil, brightness and twilight factor should not be taken to serious since all binoculars are treated the same no matter the lens coating or optical quality.
Binocular Twilight Factor
How to Choose Binoculars by their Twilight Factor [Back to Top]

The largest impact on the resolution and detail of an image is determined by the amount of light available during observation. The normal size of a users pupil during the day is from 2 to 3mm and at night it dialates from 6 to 8mm. Magnification plays an important factor on image resolution during the day and the objective lens plays an important factor at night. In twilight, both of these conditions play an important role in the effectiveness of the image resolution.

When buying binoculars, pay attention to the twilight factor if it's important to you. Use the calculations in the picture on the right. Remember, the higher the twilight factor, the better the resolution will be under low light conditions.

For example, the Zeiss Conquest 8x30 Binocular has a twilight factor of 15.5 and an exit pupil of 3.75mm; the Zeiss Conquest 10x30 Binocular has a twilight factor of 17.3 and an exit pupil of 3mm. The Zeiss 10x30 would be the better choice under low light conditions even though the 10x30 has a smaller exit pupil.

When buying binoculars, choosing binoculars by the exit pupil, brightness and twilight factor should not be taken to serious since all binoculars are treated the same no matter the lens coating or optical quality.
Binocular Interpupillary Distance
How to Choose the right Interpupillary Distance [Back to Top]

The interpupillary distance is the distance between the pupil of the eyes measured from centre to centre. When buying binoculars, they all have the capability to expand into different sizes in order to receive the correct focus. Look at the image to the right, if the binoculars exit pupils don't line up with your pupils, a shadow will cut off part of the image.

If you're not sure what your interpupillary distance measurements are, look through a pair of old binoculars, set them to where the feel comfortable within the eye space, and then measure the distance between the centres of its exit pupils.
Dioptor Adjustment
How to Choose Binoculars Diopter Adjustment [Back to Top]

The diopter adjustment allows you to change the focus of the eyepiece so that the left eye matches the right eye during observation. This feature is great since most people who buy binoculars have one eye stronger than the other.

The classic common diopter adjustment lets you adjust the focus by simply turning one eyepiece. The downside is, no locking mechanism exists to hold the adjustment in place on the lower end binoculars. The more high end, advanced binoculars such as the Zeiss Victory FL Binoculars, do have locking mechanisms. This allows you to set the diopter adjustment and not worry about loosing your setting.
Field of View
How to Choose Binoculars Field of View [Back to Top]

Field of view is a significant factor when buying binoculars. The definition of the binocular Field of View is the distance from left to right when looking through binoculars. When choosing binoculars, the higher the magnification, the smaller the field of view becomes. For example, the Vortex 8x42 Viper Binocular with a magnification of 8x, will have a field of view of 347 feet @ 1,000 yards and a Vortex 12x42 Viper Binocular with a magnification of 12x, will have a field of view of 267 feet @ 1,000 yards. As you see, the lower the magnification is the wider your field of view will be.

There's two ways to measure the field of view. One example to the right shows where it's measured in feet. The other is measured the same way but in angular degrees. One degree of an angle is equaled to 52.5 feet at 1,000 yards. Look at the picture to the right, the binoculars have an angular degree of 6 at 1,000 yards. To convert that into feet, multiply 52.5 x 6 = 315 feet.

Remember when choosing binoculars, the higher the magnification is, the smaller the field of view will become.
How to Choose Binoculars Lens Coating [Back to Top]

When choosing binoculars, the Lens Coating can easily determine the clarity, resolution, contrast and quality of the image you see. The lens coating will also help you determine the overall quality when buying binoculars.

Before buying binoculars, its very beneficial to know the four types of lens coatings available. Here are the anti-reflective lens coatings and how they rate:
  • Fully Multi-Coated Lens (FMC): Rated #1 - This is considered the best lens coating on the market and produces the most brightest images of all. It contains multiple coatings on every set of internal glass surfaces.


  • Multi-Coated Lens (MC): Rated #2 - This coating will still produce quality images. One set of the internal glass surfaces are multi coated. Typically the first and last.


  • Fully Coated Lens (FC): Rated #3 - This coating produces good enough images for most people, but not for the avid outdoors-men who consistently uses them. All sets of internal glass surfaces contain only one single coating.


  • Phase Coated Lens - These are found on the most popular roof prism binoculars such as Zeiss binoculars. It's basically a chemical coating thats applied to the prisms in order to enhance the resolution and contrast.
Remember, when buying binoculars that the lens coating will determine the overall quality.
Binocular Eye Relief
How to Choose Binoculars Eye Relief [Back to Top]

Eye Relief is the maximum distance the human eye can be from the eyepiece and still see the whole picture. This feature is most popular for people who wear eyeglasses.

Understanding eye relief is an important factor when choosing binoculars. Here is how to choose the following sizes:
  • 12-13mm - Choose this size if you have thin lenses in your glasses.


  • 14-15mm - Choose this size if you have average size lenses in your glasses.


  • 17-20mm - Choose this size if you have large lenses in your glasses.


How to Choose Binoculars Weight [Back to Top]

The binocular's weight can be an important factor when choosing binoculars. The weight has several different factors that affect it, such as the glass, the lens, the prism, the housing material and much more.

Keep in mind the activity you'll be using the binoculars for the most. If you're going on long hiking trips, most optic users find 30 ounces or below is the best weight when carrying around your neck.

The binoculars that are labeled "Compact", are extremely lightweight & durable. Some have a folding mechanism allowing them to fit directly into your pocket, others are already small enough to fit in your pocket and don't need a folding feature.
Binocular Focus Dial
How to Choose Binoculars Focus [Back to Top]

Before buying binoculars, there are 3 different focusing labels to know about. Here is a list of different focusing systems that optic manufactures offer:

  • Center Focusing Binocular - usually located in the center of the binoculars. This is the most popular focusing system because it's easy to use and allows you to comfortably focus on your target over both short and long distances.


  • Individual Eyepiece Focusing - a focusing system that's used for medium to long range distances and mostly used in marine binoculars. In order to focus on an object, it's required to focus each individual eyepiece which can become a hassle.


  • Focus Free - a focusing system that cannot be adjusted. The downfall to these are the eyepieces are locked, can't focus on targets more than 40 yards, and it has no diopter adjustment which would allow adjusting of the strength between both eyes.


Binocular Prisms
How to Choose Binoculars Prisms [Back to Top]

A Prism helps produce the images you see in the binocular. Without a prism, the binocular would show upside-down images. The two types of binocular prisms are roof and porro. Porro prisms and roof prisms are always identifiable from each other. Look at the picture to the right of the two Nikon binoculars. The porro prism binocular is much larger and bulkier. The roof prism is more compact & lightweight.

  • Porro Prism - is an older and much larger prism than a roof prism. In a porro prism binocular, the objective lens are widely spaced from the eyepieces and never in a straight line like a roof prism. Porro prisms are very efficient and cheaper than roof prism binoculars. A good quality porro prism offers a wide field of view along with a three dimensional image.


  • Roof Prism - has the objective lenses and eyepieces positioned in a straight line. The advantages of roof prism binoculars are more compact, easier to hold, and precisely aligned. The disadvantage is price. Just like with most optical devices, you get what you pay for. The roof prism is definitely more rugged, easier to focus, and quality performing system compared to the porro prism.