If you’ve ever shopped for binoculars, you’ve seen those two numbers separated by an ‘x’, like 8×42 or 10×50. But what do the numbers mean with binoculars? Understanding them is the key to choosing the right pair for your needs. It’s simpler than it looks, and this guide will explain everything in plain language.
Those two numbers tell you about magnification and light gathering. The first number is the magnification power. The second number is the diameter of the objective lenses in millimeters. Together, they define the binoculars’ performance in terms of how close things appear and how bright the image will be, especially in low light.
What Do The Numbers Mean With Binoculars
Let’s break down the two numbers you see on every binocular model. They are the most basic and important specification.
The First Number: Magnification (The “Power”)
The number before the ‘x’ is the magnification. For example, in 8×42 binoculars, the ‘8’ means objects will appear eight times closer than they do with your naked eye. A bird 80 feet away will look like it’s only 10 feet away.
- Common Magnifications: 8x and 10x are the most popular for general use. You’ll also see 7x, 12x, and higher.
- Higher isn’t always better: More magnification (like 12x or 15x) makes the image bigger, but it also amplifies hand shake, making the view shakier. They are often heavier and need a tripod for a steady view.
- Lower Magnification Pros: Binoculars with 7x or 8x power offer a wider field of view, a brighter image, and are easier to hold steady.
The Second Number: Objective Lens Diameter
The number after the ‘x’ is the diameter of the large front lenses, measured in millimeters. In 8×42 binoculars, each front lens is 42mm across. This number is crucial for light gathering.
- More Light: Larger objective lenses (like 42mm, 50mm) collect more light, resulting in a brighter image. This is vital for dawn, dusk, or forest birding.
- Size and Weight Trade-off: Larger lenses mean a bigger, heavier binocular. A 8×32 model will be more compact and lighter than a 8×42 model.
- Common Sizes: 32mm (compact), 42mm (full-size), 50mm+ (low-light specialists).
Putting Them Together: Key Specifications
The combination of these two numbers creates other important specs you should know.
Exit Pupil
This is a measure of image brightness. You calculate it by dividing the objective lens size by the magnification. For 8×42 binoculars: 42 ÷ 8 = 5.25mm.
- A larger exit pupil (over 4mm) is better for low-light conditions.
- A smaller exit pupil (under 3mm) is fine for daytime use but may seem dim at dusk.
Field of View
This is the width of the area you can see through the binoculars, usually measured in feet at 1,000 yards. It’s often listed on the box.
- General Rule: Lower magnification usually means a wider field of view. This makes it easier to find and follow moving objects, like birds or athletes.
- A wide field of view is great for scanning landscapes or watching sports.
Twilight Factor
This is a mathematical formula (√(Magnification x Objective Diameter)) that attempts to quantify performance in low light. A higher twilight factor suggests better detail resolution at dawn or dusk, but exit pupil is often a more practical guide for brightness.
How to Choose the Right Numbers for You
Now that you know what the numbers mean, here’s how to match them to your activity.
- Birdwatching & General Use: 8×42 is the gold standard. It offers a great balance of magnification, brightness, and a steady view. A 10×42 gives more detail but is slightly harder to hold perfectly steady.
- Hiking & Travel: 8×32 or 10×32. The smaller 32mm objective lenses make the binoculars much lighter and more compact, sacrificing only a little low-light performance.
- Sports & Concerts: 7×35, 8×40, or 8×42. A wide field of view is key here to follow the action. Good light gathering is also important for indoor arenas or night games.
- Astronomy & Low-Light: 10×50 or 12×50. The large 50mm lenses gather maximum light for viewing stars, planets, or wildlife at dusk. A tripod is highly recommended for magnifications over 10x.
- Marine Use: 7×50 is classic. The 7x magnification is easy to hold steady on a moving boat, and the huge 50mm lenses provide an extremely bright image and large exit pupil.
Other Important Marks on Your Binoculars
You might see other numbers and codes. Here’s a quick guide:
- Field of View: e.g., “362ft/1000yds”. This tells you the width of the view.
- Close Focus: The minimum distance at which the binoculars can focus. Important for butterfly or insect watching.
- Eye Relief: A distance in millimeters (e.g., 16mm). This is critical for eyeglass wearers. You need longer eye relief (16mm+) to see the full field of view with glasses on.
- Waterproofing: Look for designations like “Waterproof” or “IPX7.” Nitrogen or argon purging prevents internal fogging.
Quick Tips for Testing Binoculars
Before you buy, try this simple check list.
- Look at a sign with sharp lettering from across the store. Is the image clear and sharp to the edges?
- Check the focus wheel. Is it smooth and easy to turn?
- If you wear glasses, fold down the rubber eyecups and see if you can get the full picture.
- Hold them up for a minute. Do they feel to heavy or comfortable in your hands?
FAQ: Your Questions Answered
What does 10×50 mean on binoculars?
It means 10x magnification and 50mm objective lenses. They bring objects 10 times closer and have large lenses for very bright images, ideal for low light but they are larger and heavier.
Are 12x binoculars good?
12x binoculars are good for specific uses where detail is critical over long, static distances, like certain types of wildlife observation from a blind. However, they are very difficult to hold steady without support, and often have a narrower field of view. They are not generally recommended for beginners or as an all-around pair.
Which is better 10×42 or 10×50?
The 10×50 will have a brighter image due to its larger lenses, making it better for low-light conditions. The 10×42 will be more compact, lighter, and easier to carry. For most daytime use, the 10×42 is sufficient and more portable. For astronomy or dusk viewing, the 10×50’s extra light is beneficial.
What is the best all around binocular magnification?
For most people, 8x magnification is considered the best all-around choice. It provides a good balance between image size, field of view, and ease of holding steady. Paired with 42mm lenses (8×42), it works well in a wide variety of situations from birding to sports.
Can I use binoculars with glasses?
Yes, but you must look for binoculars with long eye relief (typically 16mm or more). You will also need to twist down the rubber eyecups so your glasses can get close enough to the ocular lenses to see the full field of view. Always test them if possible.
Understanding what the numbers mean with binoculars takes the confusion out of shopping. Remember, the best binoculars for you are the ones that fit your primary activity, feel comfortable in your hands, and provide a clear, bright view that you enjoy using. Now you have the knowledge to find your perfect pair. Start by thinking about where you’ll use them the most, and use the number guide above to narrow your search.