All About The View: How Binoculars Are Measured

But what, exactly, do those magnifications mean, and how are they measured?

Understanding how binoculars are measured will help you be a better hunter. Knowing what these measurements stand for is key to choosing the right pair of binoculars for your next hunt.

The Basics of Binocular Measurements

When breaking down the various features of binoculars, there are a few different terms you should become familiar with to understand how binoculars are measured.

You will often see numbers such as 7 x 35 when looking at binoculars. What do these numbers mean?

Magnification Power

The first number, 7 in this example, is the magnification power. Magnification power tells you how many times closer an object will appear to you compared to where it is standing. If you view a deer that is 400 yards away through binoculars with a magnification of 7x, it will appear to be 57 yards away.

Objective Lens Diameter

The second number, 35 in this example, is the objective lens diameter.

The objective lens on binoculars is the lens that is farther from your eye and closer to the view you see through the binoculars. The wider the diameter, the more light is being captured by the binoculars. Higher objective lens diameters are better for lower light conditions.

Exit Pupil

The exit pupil is the amount of light that will hit the eyes when viewing things through the binoculars. This number is calculated by dividing the objective lens diameter by the magnification number.

Ideally, the exit pupil diameter would always be larger than the pupil diameter of your eyes. Eye pupil diameter can range from 1.5mm when things are very bright to over 8mm in dark conditions, depending on your eyes.

Here are some examples of exit pupil ratings from common binocular sizes to give you a real example of what you are dealing with:

• 10 x 25: These binoculars would have an exit pupil of 2.5mm, which is smaller than the eye pupil diameter in all but the sunniest of conditions
• 10 x 42: These binoculars would have an exit pupil of 4.2mm, which is a good size, larger than the eye in most scenarios
• 8 x 56: These binoculars would have an exit pupil of 7mm, which is great for dark and low light conditions as well as normal daylight times

If the exit pupil is smaller than the dilation of your eyes, you will feel as if you are looking through a small hole instead of seeing a complete field of vision.

Size

In addition to having magnification and object lens diameter number specifications, most binoculars are also rated with a general size to give you an idea of what type of situations they are most useful for.

Compact Binoculars

Compact binoculars are small, light, and intended for short-term outdoor usage. They typically have a relatively high magnification rating but a small diameter, making them ideal for daylight situations.

Mid-size Binoculars 

These binoculars are great for the outdoors man who is willing to carry a moderate load in exchange for a better payoff when it comes to cloudy or dark conditions.

These binoculars come in a variety of magnification ratings and typically have at least a 32mm objective lens diameter. These are the most popular size for hunters and other outdoors sportsmen.

Full-size Binoculars

Full-size binoculars are very heavy, and they are intended for use when you will be staying in one position, such as when you are bird watching or on a boat. These binoculars perform fantastically in low-light scenarios, and they tend to have a wide view field.

Choose A Pair Best for Your Specific Needs

Now that you know how binoculars are measured, you can begin to understand what specifications you might need for your outdoor activities.

Here are the three primary facts that you need to remember:

• The farther you need to see, the more magnification power you need
• The more light you need to capture, the higher of an objective lens diameter you need to have
• The later at night you plan to use them, the higher the objective lens diameter and exit pupil rating need to be

For example, an 8 x 25 pair of binoculars has more magnification and less light-capturing power than a 7 x 32 pairs. Many hunters who plan to hunt in early morning or light night hours find that the 8 x 56 rated binoculars tend to perform best for them.

No matter what your specific needs are, understanding magnification, objective, and exit pupil ratings will help you find the perfect pair of binoculars.