If you’re new to binoculars, the numbers on them can seem like a secret code. Understanding what are the numbers for binoculars is the first step to picking the perfect pair for your needs. These figures tell you everything about magnification, brightness, and field of view, so you can make an informed choice.
Let’s break down what those numbers mean and how they effect your viewing experience. You’ll be able to read any binocular specification with confidence.
What Are The Numbers For Binoculars
The most common numbers you’ll see look like this: 8×42, 10×50, or 12×25. This is the binocular’s model number, and it holds the two most critical pieces of information: magnification and objective lens size. The first number is always the magnification, and the second is the diameter of the objective lens in millimeters.
The First Number: Magnification Power
The number before the “x” is the magnification. An 8×42 binocular makes objects appear eight times closer than they do to your naked eye. A 10×50 makes them appear ten times closer.
- Common Magnifications: 8x and 10x are the most popular for general use. Lower powers like 6x or 7x offer a wider view and are great for theater or sports. Higher powers like 12x or 15x are used for long-distance observation but can be harder to hold steady.
- Trade-off: Higher magnification narrows your field of view and amplifies hand shake. For most people, 8x or 10x provides the best balance.
The Second Number: Objective Lens Diameter
The number after the “x” is the diameter of the front (objective) lenses in millimeters. Larger lenses gather more light, which results in a brighter image, especially in low-light conditions.
- Common Sizes: 20mm to 50mm are typical. Compact binoculars often have lenses 25mm or smaller. Full-size binoculars usually start at 42mm.
- Brightness Factor: A 42mm lens gathers more light than a 25mm lens, making a 8×42 binocular better for dawn, dusk, or forested areas than a 8×25 model.
Key Specifications Derived from the Numbers
From the two main numbers, we can calculate other important specs that effect performance.
Exit Pupil
This measures the width of the beam of light that exits the eyepiece and enters your eye. You calculate it by dividing the objective lens diameter by the magnification.
- Formula: Objective Lens / Magnification = Exit Pupil (in mm).
- Example: 42 / 8 = 5.25mm exit pupil.
- Why it Matters: In low light, your eye’s pupil dilates to about 5-7mm. An exit pupil of 5mm or larger is ideal for low-light use. For daytime, a smaller exit pupil (around 2-3mm) is sufficient.
Field of View
This is the width of the area you can see through the binoculars at a specific distance, usually expressed in feet at 1000 yards or degrees. Generally, lower magnification gives a wider field of view.
- Example: An 8x binocular might have a field of view of 400 feet at 1000 yards, while a 12x might only show 250 feet. A wider field makes it easier to follow moving objects like birds or athletes.
Relative Brightness & Twilight Factor
These are older, less critical metrics, but you might still see them. Relative Brightness is the exit pupil squared (e.g., 5.25² = ~27.6). Twilight Factor is calculated as the square root of (Magnification x Objective Lens). They attempt to quantify low-light performance, but exit pupil and lens quality are more practical guides.
How to Choose the Right Numbers for You
Your ideal binocular depends on what you plan to use it for. Here’s a simple guide based on activity.
- Birdwatching & Wildlife: 8×42 is the gold standard. It offers a good balance of magnification, a bright image, and a wide enough field to find and track animals. 10×42 is also excellent for more open areas.
- Hiking & General Outdoor Use: Compact models like 8×25 or 10×28 are lightweight and easy to carry. Their smaller objective lenses are a trade-off for portability.
- Astronomy & Low-Light: Prioritize large objective lenses. Models like 7×50, 10×50, or even 10×56 gather maximum light for viewing stars or wildlife at dawn and dusk.
- Sports & Concerts: Lower magnification with a wide field is key. Look for 6×30, 7×35, or 8×32 to easily follow the action without to much shake.
- Marine & Long-Distance Observation: Higher magnification like 10×50 or 12×50 can be useful, but consider image-stabilized models if you’ll be on a moving boat.
Other Important Markings to Understand
Beyond the main numbers, you might see other letters and figures on the binoculars body.
- Eye Relief (in mm): This is crucial for eyeglass wearers. It’s the distance your eye can be from the eyepiece and still see the full image. Look for 15mm or more if you wear glasses.
- Close Focus (in feet/meters): The minimum distance at which the binoculars can focus. Important for butterfly watching or looking at details on close objects.
- Waterproofing (WP, Waterproof): Indicates sealed optics to prevent internal fogging and damage from moisture.
- Armor (Rubber Armor): A rubber coating that provides shock resistance and a secure grip.
Putting It All Together: A Simple Checklist
When you’re ready to buy, walk through these steps.
- Define Your Primary Use: Pick your main activity from the list above to narrow down the magnification and lens size.
- Check the Fit: Hold the binoculars. Are they comfortable? Can you adjust the eyecups easily if you wear glasses? Is the focus wheel smooth?
- Test the View: If possible, look through them. Is the image sharp and bright to the edges? Is the field of view satisfying?
- Consider Your Budget: Often, optical quality (lens coatings, glass precision) matters as much as the numbers. A well-made 8×42 will outperform a cheap 12×50 every time.
Frequently Asked Questions (FAQ)
What does 10×50 mean on binoculars?
It means the binoculars have 10x magnification, making objects appear ten times closer, and have objective lenses that are 50mm in diameter. This is a common size for activities needing a bright image, like astronomy or low-light wildlife viewing.
Are higher magnification binoculars better?
Not always. Higher magnification (like 12x or 15x) makes image shake more noticeable and narrows your field of view. For most handheld uses, 8x or 10x provides a better, more stable veiwing experience.
What is the best all-around binocular size?
The 8×42 binocular is widely considered the best all-purpose size. It offers strong magnification, a bright image with a good exit pupil, and a reasonably wide field of view, making it versatile for birding, sports, and general nature observation.
What do the numbers on binoculars mean for light gathering?
The second number (objective lens diameter) directly effects light gathering. Larger lenses (e.g., 42mm, 50mm) let in more light than smaller lenses (e.g., 25mm), resulting in a brighter image, which is especially important in dim conditions.
Is 10×42 better than 8×42?
It depends. The 10×42 brings objects 25% closer but has a slightly narrower field of view and shows more hand shake. The 8×42 offers a wider, steadier view. Choose 10x for more power in stable conditions (like using a tripod) or 8x for a more relaxed, handheld view.
Now you can decode any pair of binoculars. Remember, the best binocular for you is the one whose numbers match your favorite activities and feels comfortable in your hands. Take your time to compare, and you’ll find a pair that brings the world wonderfully closer.