If you’ve ever picked up a pair of binoculars, you’ve probably wondered what does the numbers on binoculars mean. Those figures, like 8×42 or 10×50, are the key to understanding their performance. They tell you everything about magnification, brightness, and field of view. Knowing how to read them is the first step to choosing the perfect pair for your needs.
What Does The Numbers On Binoculars Mean
The numbers on binoculars are a standardized way of describing their two most important optical specs. You’ll usually see two numbers separated by an “x,” such as 8×42. The first number is the magnification. The second number is the objective lens diameter. Together, they give you a clear picture of what the binoculars can do.
Breaking Down the First Number: Magnification
The number before the “x” is the magnification power. It tells you how many times closer an object will appear compared to viewing it with your naked eye. For example, in an 8×42 model, objects will look eight times closer.
- 8x Magnification: An object 800 feet away will look like it’s only 100 feet away.
- 10x Magnification: The same object would appear just 80 feet away.
Higher magnification isn’t always better. While it brings subjects closer, it also amplifies hand shake, making the image shakier. It often means a narrower field of view and less light gathering. For general use, magnifications of 7x to 10x are most common and versatile.
Understanding the Second Number: Objective Lens Size
The number after the “x” is the diameter of the objective lenses (the lenses farthest from your eyes) measured in millimeters. In our 8×42 example, each front lens is 42mm wide. This number is crucial for image brightness.
- A larger objective lens (e.g., 42mm, 50mm) collects more light. This results in a brighter, clearer image, especially in low-light conditions like dawn or dusk.
- A smaller objective lens (e.g., 25mm, 32mm) makes the binoculars more compact and lightweight, but the image may be dimmer in poor light.
The size of these lenses directly impacts the weight and portability of the binoculars. Bigger lenses mean more glass, which adds weight.
The Critical Relationship: Exit Pupil
Magnification and lens size work together to create the exit pupil. This is the small circle of light you see in the eyepiece when you hold the binoculars away from your face. You can calculate it easily: just divide the objective lens diameter by the magnification.
For 8×42 binoculars: 42 ÷ 8 = 5.25. The exit pupil is 5.25mm.
Why does this matter? Your eye’s pupil also dilates and contracts with light. In bright daylight, your pupil might be only 2mm wide. In dark conditions, it can open to about 7mm. For low-light viewing, you want a binoculars exit pupil that matches or exceeds your eye’s dilated pupil (around 5mm or larger) for the brightest view.
Field of View: The Third Key Spec
Often listed in the specifications, the field of view (FOV) is how wide an area you can see through the binoculars at a specific distance, usually expressed in feet at 1,000 yards or degrees. It’s heavily influenced by magnification.
- Lower magnification (e.g., 7x or 8x) typically gives a wider FOV, making it easier to follow moving subjects like birds or athletes.
- Higher magnification (e.g., 12x or 15x) usually has a narrower FOV, which can make it harder to locate and track objects.
Other Numbers and Codes You Might See
Binoculars sometimes have additional letters and numbers that provide more information about their design.
- Close Focus: A number like “6.5ft” tells you the minimum distance at which the binoculars can focus sharply. Essential for butterfly or nature observers.
- Eye Relief: A number like “18mm” indicates the distance your eye can be from the eyepiece and still see the full image. Critical for eyeglass wearers; look for 15mm or more.
- Waterproof Ratings: Codes like IPX7 mean the binoculars can withstand immersion in water to a certain depth for a certain time.
- Prism Type: You may see BAK-4 or BK-7. BAK-4 glass is higher quality, offering sharper images and rounder exit pupils.
How to Choose the Right Numbers for Your Activity
Matching the numbers to your primary use makes all the difference. Here’s a simple guide:
- Birdwatching & General Wildlife: 8×42 is the gold standard. It offers a great balance of magnification, a bright image, a wide field of view, and manageable weight. 10×42 is also popular for more open areas.
- Hiking & Backpacking: Prioritize compact size and light weight. Look for 8×32 or even 10×28 models. The smaller objective lenses save on bulk.
- Marine & Astronomical Use: Here, light gathering is key. Choose larger objective lenses like 7×50 or 10×50. The 7×50 model, with its huge 7.1mm exit pupil, is legendary for low light.
- Sports & Concerts: A wide field of view is helpful for following the action. Lower magnifications like 7×35 or 8×32 work well in typically well-lit venues.
- Stargazing: A steady tripod is often needed for higher magnifications. Consider 10×50 or 15×70 models on a tripod for detailed celestial viewing.
Common Mistakes to Avoid When Interpreting Numbers
Don’t get caught up in common pitfalls. First, avoid thinking bigger magnification is always the best choice. A 12x or 15x binocular will be very hard to hold steady without a tripod, leading to a frustrating, shaky image. Second, remember that compact binoculars with small lenses (like 8×21) are great for pocketability but will struggle in dim light. Finally, always check the eye relief number if you wear glasses. A long eye relief spec is essential for a full view without removing your glasses.
Putting It All Together: A Quick Checklist
Before you buy, run through this simple list:
- For versatility, 8×42 is a safe, highly recommended starting point.
- Calculate the exit pupil (Objective Lens ÷ Magnification) – aim for 4mm or higher for general use.
- Check the field of view spec if you need a wide view.
- Ensure the eye relief is 15mm+ if you wear eyeglasses.
- Match the size and weight to your activity—will you be carrying them for hours?
Understanding what the numbers mean empowers you to make a smart choice. You’ll be able to look past marketing terms and select a tool that truly fits how you plan to use it. The right pair of binoculars can bring the world dramatically closer, revealing details you’d otherwise miss.
FAQ Section
What do the numbers 10×50 mean on binoculars?
It means the binoculars have 10x magnification and 50mm diameter objective lenses. They make objects appear 10 times closer and are excellent for low-light conditions due to the large light-gathering lenses.
Which is better, 8×42 or 10×42 binoculars?
It depends on use. 8×42 offers a wider field of view, brighter image (larger exit pupil), and is easier to hold steady. 10×42 brings subjects closer but with a slightly narrower, shakier view. 8×42 is often recommended for general and birding use.
What does the second number on binoculars mean?
The second number is the diameter of the objective (front) lenses in millimeters. It determines how much light the binoculars can collect, which affects image brightness, especially in poor lighting.
Are higher magnification binoculars better?
Not necessarily. While they offer more “closeness,” they also magnify hand movement, have a narrower field of view, and can be heavier. For handheld use, magnifications above 10x or 12x often require extra support like a tripod for a clear view.
What do binocular numbers mean for eye relief?
Eye relief is a separate number (e.g., 18mm) listed in the specs, not in the main “8×42” style marking. It tells you how far your eye can be from the eyepiece. A longer eye relief (15mm+) is vital for comfortable viewing with eyeglasses.