How to Choose Binoculars, According to Science – 15 Factors to Consider

binoculars 431488 640
If you have spent a lot of time searching for binoculars, did you do your research well? Understanding the key aspects of what makes a binocular is essential. Then you know what to look for and how. To be honest, binoculars aren’t that easy to track down, especially when you want something specific.

So I’ve peered through the basics of a binocular and how they influence certain applications. This guide is the culmination of that research and it’s a decisive one, to be fair. By the end of this guide you know will inside out the features of the best binoculars to look out for.

Even if you plan on using it once a week or through the season, you really should consider the following factors before trying out a rugged binocular for your own personal use. (1)

1. Which Binocular Size Is Best?

Binoculars are available in a number of sizes based on the type of use and convenience. There are 3 main sizes including full-size, mid-size, and compact binoculars.

Full-size binoculars: Binoculars that fall under this category offer more light and attention to detail, especially under low-light situations. The objective lens size on full-sized binoculars is the largest, offering better field view and precision.

It’s self-evident that full-sized binoculars are the most heavyweight binoculars to buy. So holding the binocular for a long time might seem a big too much after some time. Big-game observers and professionals make use of full-size binoculars, usually with a tripod for better usability. These also come with higher magnification than other models.

Mid-size binoculars: Binoculars under this category offer the features of both full-size and compact binoculars. The magnification and light transmission capacity is well-balanced for intermediates for sport and wildlife use.

Compact binoculars: Compact binoculars are best used for backpackers and for general use. They’re the most lightweight binoculars with smaller objective lens and lesser magnification strength.

Using a compact binocular for long might be unsatisfactory due to its compact size which is difficult to hold. Professionals often use compact binoculars as a back-up for full-sized ones. For general outdoor pursuits, using a compact binocular is well-suited.

After knowing this, can you not decide which is the best size for you? I’m sure you can! To find an easy-to-hold binocular after eliminating the ill-fitting ones is a good way to start.

Using a comfortable binocular is the first step toward making the right purchasing decision. It is easy to carry, pack, and hold for long periods. However, full-sized binoculars offer higher magnification and objective lens size which is makes viewing much more clear and detailed.

Making a clear distinction between features and size is a matter of personal preference, especially when searching for a rugged binocular.

2. Selecting The Magnification Power

The size of a binocular and its magnification power and objective lens diameter go hand-in-hand. But it’s important for you to know what the magnification power of any binocular stands for. (2)

The first thing you should know is that binoculars are categorized based on 2 primary numbers. The first number is the magnification power paired up with the objective lens size of a binocular.

For example, a full-sized binocular is specified as 10 x 50 where the number before the “x” is the magnification power and the other number is the objective lens diameter. In simple words, the magnification power of a full-sized binocular is 10 times more powerful. It can also be said that images through this binocular appear 10 times closer.

Binoculars come with a magnification power of 3 to 4 or 7 to 10. Anything higher than 10 is used by serious professionals for wildlife or sports use.

Based on one report, using higher magnification, that is above 10 offers clear sight, but limited low-light compatibility. They’re also very difficult to hold steady, unless attached to a sturdy tripod. (2)

Using a binocular with a magnification power of 7 to 9 is most suitable. It offers high-quality light transmission, for both bright and low-light conditions.

There are many different binoculars with fixed-magnification or adjustable zoom magnification settings. But is buying the highest magnification better?

Using high magnification reduces the area covered by the magnification power measure. For example, if you use a binocular with 30x magnification, finding and targeting a bird would take a longer time. And during that time, the bird might have flown away before you have located it.

Another disadvantage of using higher magnification when it’s not required is light transmission. Increased magnification reduces the amount of light entering the lens. So you will end up with a dark, blurry, and extremely zoomed-in view when you use an increased magnification binocular.

For objects even further away, consider getting the best telescope instead. 

3. Selecting The Objective Lens Size

As mentioned above, binoculars come with 2 primary numbers. The magnification power and the objective lens diameter. (3)

In the case of a full-sized binocular, 10 x 50, the objective lens diameter of that particular binocular is 50 millimeters. According to this theory, the higher the objective lens diameter, the more light it is able to transmit and gather. So if you want something that works in low-light conditions, using a binocular with a higher objective lens size is suitable.

The diameter of the objective lens determines the total amount of light that enters into the binoculars. If you buy two similar binoculars with different objective lens size, the one with the higher size will be able to capture more light than the one with a lower objective lens diameter.

No other aspect of the binocular or the image perceived through it are influenced by the objective lens diameter. In simple words, the larger the diameter, the heavier the binoculars, regardless of the magnification power of it.

The standard objective lens diameter of binoculars ranges from 20 to 50 millimeters. But if you’re buying a binocular for pure astronomical use, buying above 100 millimeters is normally suitable. This makes the binocular heavier to hold, so the use of a tripod is needed.

If you’re looking for a standard binocular, finding something between 25 millimeters to 40 millimeters is sufficient. It offers plenty of light transmission, isn’t too heavy to hold, and is durable.

4. What’s The Exit Pupil?

Based on the magnification power and objective lens can you determine the exit pupil of a binocular. The way to calculate is by dividing the objective lens diameter by the magnification power.

For example, with a full-sized binocular, 10 x 50, the exit pupil would be 50 divided by 10. The answer is a 5-millimeter diameter of the beam of light that reaches your pupil or eye. Hence, it’s called the exist pupil.

In comparison, the higher the exit pupil diameter of any binocular, the more light enters into the binocular and meets your eye.

According to Science Daily, the human eye dilates to 1.5 millimeters in bright day-light and up to 8 millimeters in lower-light conditions. (4)

In other words, the higher the exit pupil diameter, the simpler it is for the eyes to focus on an object without any distractions. So even if your hands (or the object) shake or shift a bit, it won’t make any difference.  

For bright light conditions: Considering a binocular with a higher or lower exit pupil isn’t necessary. For daylight viewing only, the human eye dilates 2 millimeters. So finding a binocular with an exist pupil of 2 or higher is not that difficult.

For dim light conditions: Considering a binocular with a higher exit pupil is necessary. Anything above 5 millimeters is considered ideal for viewing in low-light situations such as dawn, dusk, or night-sky.

But based on one report, it can also be said that human eye can dilate to 9.5 millimeters for professional bird watching. But the ideal exit pupil for most bird watchers is about 5 millimeters. (5)

5. How Far Can You See?

This factor is as important as the binocular’s magnification power, objective lens diameter, and exit pupil. It dictates the field of view of the binocular, which is measured in either meters or feet. (6)

There are 2 main types of field of view, real and apparent field of view.

Real field of view: The real field of view is the actual distance you view at a single glance. It’s measured in at 1,000 meters from where you stand. Imagine a fence opposite the center view of the binoculars. And the total area or length of the fence you see, in either feet or meters, is the real field of view of that particular binocular.

The wider the field of view, in this case, the more objects you can identify. The rule of the thumb is that the higher magnification on a binocular, the smaller the field of view. And vice versa.

Apparent field of view: This is also known as angular field of view which is measured in degrees. Unlike the read field of view, the apparent field of view dictates the width of the view that’s seen through the binoculars.

To determine the apparent field of view of a binocular, you need to multiply the real field of view (convert into degrees) by the magnification power of the same binocular. That will give you the apparent field of view, in degrees.

For example, a binocular’s magnification power is 8x and its real field of view is 472m at 1000m. To determine the apparent field of view, convert the real field into degrees, which makes it 7.4 degrees. So the multiplication of 8 by 7.4 results in an apparent field of view that is 59 degrees.

The highest apparent field of view measure is about 75 to 80 degrees. Anything higher than this leads to distorted and unclear images.

6. Roof Prism or Porro Prism - Which Is Better?

Binoculars can also be chosen based on their design type: roof prism and porro prism. The common word “prism” in both these types refers to the manner in which each type channel light through its lens to your eyes. (7,8)

Buying either one is a matter of personal preference. The fact is that roof prism binoculars have taken over the market. The reason being they’re comparatively simpler and straightforward (literally) to use than porro prisms.

The light enters the binoculars in a straight line and passes a straight plane so the user can see a more streamlined shape of the binoculars. This gives a roof prism the upper edge. However, roof prisms do lack 100% light reflection features, unlike a porro prism. The prism doesn’t reflect all the light entering the path, resulting in a less bright and clear image.

A porro prism looks like the letter “M” while a roof prism has a traditional “H” shaped design. In a porro prism, the light entering the path doesn’t run on a straight path toward the eyes. This means the lens and the eyepiece are not in a straight line.

Choosing either one also depends on the price. If you don’t mind investing in something upgraded, buying a roof prism equipped with reflective glass and phase correction features is more effective than paying for a standard porro prism.

That said, roof prisms are more expensive to buy than porro prism, despite the straightforward design. Hence, if you’re looking for something effective and affordable, buying a porro prism is good enough. (9)

7. Understanding Binocular Lens Coatings

If some of the light entering the binocular is reflected away from the lens, it can result in an unclear and dim image. The lens cut down the total amount of light passing through it. So to correct such an issue, certain types of coatings are applied on the lens to reduce reflection.

The result is a lens that fully transmits the light rather than reflecting it away from the viewer’s eye. Binocular lenses are made up of either plastic or glass. Glass lenses offer incredible quality and are most expensive than plastic lenses. Also, they’re more likely to reflect light than plastic ones.

Nevertheless, there are varied types of lens coating that can reduce reflection and increase overall light transmission. These coatings also help in removing glare for the clearest and brightest image quality. (10)

Coated (C): Coated lenses, commonly marked as “C”, is the most basic coating. If your binocular has coated lenses, it means that there is only a single layer of coating on the lens.

Multi-coated (MC): Multi-coated lenses, commonly marked as “MC”, means multiple layers of coating on at least one lens inside the binocular.

Fully-coated (FC): Fully-coated lenses, commonly marked as “FC”, means a single layer of coating on all air-to-glass lenses or surfaces.

Fully multi-coated (FMC): Fully multi-coated, commonly marked as “FMC”, is the combination of multi- and fully-coated lenses. It’s when there are multiple layers of coating on all air-to-glass lenses or surfaces.

In hindsight, MC and FMC are superior to C and FC in terms of quality and price. But they dramatically reduce the light reflection in glass lens binoculars and enhance light transmission. FMC surfaces come with coatings on both sides, that is the inner and outer surface. This means there’s better clarity, attention to detail, contrast, and color quality.

The use of plastic in binoculars is impractical and ineffective. It causes more light loss than glass and they do not bode well with lens coating. (11)

8. What About Focusing?

The center focus system is the most common focus system on a binocular. It comprises of a primary focus wheel that sits between the two binocular lenses. Some binoculars come with an adjustable focus dial that you can shift right to left based on your focusing needs.

More and more binoculars are becoming specialized for expert optical inspections. This means that you can watch insects and small birds with 100% clarity and color distinction. So if you’re watching something far away, getting to the point of closest focus is essential for proper light transmission.

Individual focus models: This includes center focus systems that allow precise focusing ability on both eye-pieces of a binocular. If you’re not sharing your binocular with anyone, using an individual focus model is great enough.

This is where the diopter corrector is on one of the eyepieces to suit one person only.

Focus-free models: Like the name suggests, focus-free models lack dioptric correction and any focusing mechanism. They only depend on the magnification, objective lens, and field of view. Plus, it’s more suitable for people who’d like to focus on landscape rather than tiny objects that are far away.  (12)

However, using a focus-free model might cause eye strain when you’re trying to focus on something much closer than the field of view.

Waterproof models: Waterproof binoculars come with center-focusing mechanism, but the difference is that they feature a diopter corrector on both the eyepieces. So you can make adjustments for each lenses, for increased durability and efficiency.

9. Waterproof or Water-Resistant - Which Is Better?

Traditional binoculars lack both a waterproof and water-resistant body. Due to increased expenditure on upgraded models, now you will find waterproof and water-resistant binoculars.

Before choosing a binocular, it is important to know whether you’ll be using it in versatile weather conditions. If you plan on using it outdoors, there is a possibility that your binocular will get wet in the rain.

But if you’re taking it with you for camping, rafting, or even for fishing, it’s a whole different topic.

What’s the difference between waterproof and water-resistant? According to HZO, water-resistant products have the ability to resist water during penetration. But this is only to a certain level of penetration. A waterproof product, on the other hand, is entirely resistant or opposing to water, regardless of the level of insertion.

So waterproof binoculars are impervious to water. It keeps water out of the build and prevents moisture from building up near the surface. Waterproof binocular models also resist dust or debris from entering.

Water-resistant binoculars only protect against rainfall. They’re not ideal for rafting or fishing, so water penetration isn’t an option.

If you’re using your binoculars on a rainy day, away from any shallow or deep water body, buying a water resistant model is most fitting. But when you’re taking your binocular along on a boat for river rafting and bird watching, it’s best to buy a waterproof model.

10. Considering A Fog Proof Binocular

The next thing to consider, in terms of durability, is a fog proof construction. Any cheap binocular may come with features that encourage fog buildup on the surface. Water vapor or moisture can easily enter the binocular, creating fog that cloud and rust your lenses.

Buying a fog proof binocular is just as important as a waterproof binocular. It all anti-fogging elements and features that prolong shelf life and reduce condensation of water.

According to one report, when moisture comes in direct contact with dryer air, it leads to fog. This type of fog is commonly seen on both sides of the glass surface. So a major drop or difference in temperatures can lead to fog. In such a case, blaming the glass quality isn’t the right thing to do.

Once you purchase a fog proof binocular that seals the body shut, preventing any sort of contact to the outside temperature, it will solve all your problems.        

A fog proof binocular will contain nitrogen or argon gas that prevents fogging. It keeps the atmosphere inside the binocular dry and pressurized to avoid condensation and a temperature shift. This is typically done with the help of sealed O-rings and rugged gaskets. (13)

An important thing to remember is that not all waterproof binoculars come with anti-fogging elements. But it’s true that all fog proof binoculars are waterproof by nature. (14)

11. Determining Binocular Eye Relief

To make sure you don’t strain your eyes when viewing through the binoculars, both eyepieces should be at a comfortable distance from your eyes. In that way, eye relief is the total distance between the eyepiece and your eye for as long as the field of view is clear.

With a longer eye relief, you can hold the binocular away from your face while seeing the whole field of view. If you wear glasses, this is the most important factor to consider. The better the eye relief, the most comfortable you feel while holding the binocular, especially for a longer period of time.  

Some binoculars come with rubber eyecups that are installed where the eyepiece ends for better positioning and comfort. This makes the binoculars more efficient at viewing the field of view, even with longer eye relief.

Regardless of the eye relief, what you see through the binocular should be crystal clear and sharp. So considering dioptric adjustments for proper optical perception is a good way to go. That way you maintain sharp focus and you have a broad viewing area without facing any difficulties.

The optimal eye relief for binoculars is 10 millimeters. But if you’re wearing eyeglasses, the most comfortable eye relief would be at least 15 millimeters. (15)

Most of the times, consumers forget to weigh in the eye relief factor when considering a good binocular. So it’s important to measuring your most optimal eye relief measure before making a final choice. If the binoculars you already have aren’t compatible with your eye point, especially if you wear eyeglasses, upgrading to something that is is very important.

12. Deciding The Right Brightness Level

Based on the exit pupil can you decide the right relative brightness of your binocular. If the exit pupil of a binocular is 5 millimeters, then the relative brightness of that particular binocular is the square of the exit pupil.

For example, a full-sized binocular offers an exit pupil of 5mm. Square that number (5 x 5) to get the relative brightness number which is 25.

The higher the relative brightness, the clearer and brighter the image quality. Considering the relative brightness of a binocular for working under low-light conditions is essential. Low-light viewing largely depends on the exit pupil because it determines on the amount of light coming through the eyepiece.

The best binoculars for low-light situations offer a larger exit pupil, higher relative brightness, and more durable reflective coating. This allows light to enter without reflecting back and enhances light transmission to reduce eyestrain. (16)

13. Do You Need Image Stabilization?

Modern binoculars come with image stabilization features, also known as, image-stabilized binoculars. They reduce vibration for more advanced optical viewing conditions such as astronomy.

If your binocular can reduce viewing motion caused by hand movement, it can enhance image quality and precision. Some modern binoculars also excel at bringing the object you’re targeting closer due to image stabilization.

Factors such as the swaying of the boat, vibration of an aircraft, or a moving car can prevent you from steady hands. So buying image-stabilized binoculars to provide expert stabilization can reduce image disorientation. It offers high-power optics, high-quality coating, and a durable build that’ll last you for years. (17)

Ask yourself where you’ll be using your new binoculars and how. Any sort of movement can result in distorted image quality through the binocular lens. Just as how a digital camera stabilizes an image, binoculars prevent motion and vibration from interfering with the final optical perception.

14. Using A Rangefinder

Using a rangefinder binocular might be limited to only professionals, but it has plenty of features to be excited about. A study studied the effectiveness of a rangefinder binocular for mapping a landslide. (18)

For example, the best laser rangefinder uses infrared laser that helps you measure the distance between the binocular and the object you’re targeting.

This object can be a bird, insect, or an animal. Professionals use a rangefinder for hunting, golfing, and many other purposes. So if any of these relate to what you’re planning on use a binocular for, choosing a rangefinder binocular is a good choice.

You can use a rangefinder to know the exact distance of a ship from where you stand. It’s also good if you want to target an object within a few meters.

Modern binoculars come with precise updated measurements to help you calculate the distance. Some even feature downhill or uphill angles, based on how far you are from an object. You can track an object in motion while measuring the exact distance in a matter of seconds using a rangefinder binocular.

Choosing a rangefinder as an added advantage can be a great thing, but it comes at a hefty cost.

15. Looking For Accessories

Every binocular comes with basic accessories that makes it even more versatile and upgraded. Here are some basic accessories that may be a part of your binocular purchase.

Straps: Just like a digital camera, holding a binocular can be tedious. Especially when you’re using one of the full-size ones. It’s always safer to use a durable, padded, and adjustable strap with your binocular. You can hang it around your neck when you’re not using it. And grab it in a quick second when you need it.

Rain guards: Does your current binoculars’ eyecups flood every time you step out into the rain? Upgrading to rain guards is so much better. Modern binoculars feature one-piece rain guards that prevent flooding. You can even attach it to your strap to increase its shelf life to protect against unexpected rainfall.

Cleaning kit: Don’t think a binocular has self-cleaning abilities. Maintaining a binocular takes time and effort, but it’s much easier with an included cleaning kit. Wherever you’re buying a binocular from, it’s always advisable to request for a cleaning kit, unless they provide you with one.


That’s all you need to know about choosing binoculars on the market. Finding exceptionally durable and versatile binoculars that withstand dust, debris, moisture, and other elements isn’t simple. And you need to focus on small details, no matter what it is.

This guide will help you track down the best features of a binocular. Anyone who’s invested in making distant objects seem closer knows how important a good pair of binoculars are. Your binocular needs to make far-away objects appear closer and what you see through the eyepiece needs to be clear with good color quality.

If you find a binocular that can do these two things well, after you’ve considered all significant factors, you’ve finally found your match! With that in mind, are you ready to buy your next binoculars?