If you’re new to birdwatching, hunting, or astronomy, you might wonder what do the number for spotting scopes mean. Those figures, like 20-60×80, are the key to understanding a scope’s power and performance.
They tell you everything about magnification and light gathering. Getting to know them helps you pick the perfect tool for your needs. Let’s break it down into simple parts.
What Do The Number For Spotting Scopes Mean
The numbers on a spotting scope describe its two most important features: magnification and objective lens size. They are always written in a specific format, usually something like “15-45×60” or “20×80”. The first number(s) refer to magnification, and the number after the “x” is the diameter of the objective lens in millimeters.
Think of it as the scope’s basic identity. Once you can read this code, you can quickly compare different models. You’ll know what to expect before you even look through the eyepiece.
Decoding the Magnification Number
The magnification number tells you how much closer the target will appear compared to your naked eye. A scope with “20x” magnification makes an object look 20 times closer. If the scope has two numbers separated by a dash (e.g., 15-45x), it means the scope has a zoom feature.
- Fixed Magnification: A single number like 20x or 25x. These scopes are often simpler, with excellent optical clarity, but you cannot zoom in or out.
- Variable/Zoom Magnification: A range like 15-45x. This gives you flexibility. You can zoom out to find your subject easily, then zoom in for a detailed look.
Higher magnification isn’t always better. As you zoom in more, the image can become shakier and dimmer. A steady tripod is essential for high power viewing.
The Importance of the Objective Lens Size
The second number, after the “x”, is the objective lens diameter in millimeters. In a 20-60×80 scope, the “80” means the front lens is 80mm across. This is a critical spec because it determines how much light the scope can collect.
- A larger objective lens (e.g., 80mm, 85mm) gathers more light. This results in a brighter, clearer image, especially in low-light conditions like dawn, dusk, or under a cloudy sky.
- A smaller objective lens (e.g., 50mm, 60mm) means the scope is more compact and lightweight, but it will not perform as well in poor light.
This number directly impacts the scopes size and weight. Bigger lenses need bigger bodies, so there’s always a trade-off between performance and portability.
How Magnification and Lens Size Work Together
These two numbers don’t work in isolation. Their relationship creates the overall viewing experience. The key concept that links them is the exit pupil.
Exit pupil is the small circle of light you see in the eyepiece. You can calculate it by dividing the objective lens size by the magnification. For example, at 40x magnification on an 80mm scope, the exit pupil is 2mm (80 ÷ 40 = 2).
- A larger exit pupil (above 4mm) gives a bright image that’s easy to look through, even if your eye isn’t perfectly aligned.
- As you zoom in, the exit pupil gets smaller. A very small exit pupil (below 2mm) makes the image appear dim and the “sweet spot” for your eye becomes very tiny, making the image hard to see.
This is why a scope with a larger objective lens maintains a brighter image at high magnifications than a scope with a smaller lens. It’s simple math and physics.
Choosing the Right Numbers for Your Activity
Now that you know what the numbers mean, you can match them to what you’ll be doing. Different hobbies have different ideal ranges.
- Birdwatching: A versatile zoom like 15-45x or 20-60x on a 60mm to 80mm scope is excellent. You need the zoom to track birds in thickets and the light gathering for forest shade.
- Hunting & Target Shooting: Durability and clarity are key. A 20-60x80mm scope is common for long-range spotting. Some prefer a fixed 25x or 30x wide-angle scope for its steady, bright field of view.
- Astronomy & General Nature: For celestial viewing, a large objective lens (80mm+) is great for gathering starlight. A zoom eyepiece allows you to frame the moon or find star clusters easily.
- Backpacking & Hiking: Weight is the priority. A compact 50mm or 60mm scope with a zoom eyepiece (e.g., 15-45×60) offers a good balance of power and portability.
Other Important Specs Beyond the Numbers
While the main numbers are crucial, other factors affect performance. Don’t forget to consider these when choosing a scope.
- Lens Coatings: Fully multi-coated lenses are best. They reduce glare and internal reflections, increasing light transmission for a sharper, brighter image.
- Close Focus: This is the minimum distance at which the scope can focus. If you like to look at butterflies or insects, a close focus of 10 feet or less is very helpful.
- Field of View: Measured in feet at 1000 yards, this tells you how wide an area you can see. Wider fields make it easier to find and follow moving subjects. Generally, lower magnification gives a wider field of view.
- Water & Fog Proofing: Nitrogen or argon purging prevents internal fogging. This is essential for any use in humid or changing weather conditions.
A Simple Step-by-Step Guide to Reading Scope Numbers
Let’s put it all together with a simple process. Follow these steps next time you look at a scope’s description.
- Find the two-part number (e.g., 20-60×80).
- Identify the magnification. If it’s a range, it’s a zoom scope. The first number is the lowest power, the second is the highest.
- Identify the objective lens size. This is the number after the “x” in millimeters.
- Consider your primary use. Match the magnification range and lens size to your activity using the guidelines above.
- Remember the trade-offs: Higher zoom can mean a dimmer, shakier image. A bigger lens means better light but more weight.
With this knowledge, you can confidently compare models and choose a scope that fits both your eyes and your adventures perfectly. The right numbers make all the difference in the field.
FAQ Section
What does 20-60×80 mean on a spotting scope?
It means the scope has a zoom magnification from 20 times to 60 times, and it has a large 80 millimeter objective lens for gathering light.
Is a higher magnification spotting scope better?
Not always. While it brings subjects closer, higher magnification reduces image brightness, narrows the field of view, and amplifies hand shake. It often requires a very steady tripod to be usable.
What is a good objective lens size?
For most users, a lens between 60mm and 80mm offers a great balance of light gathering and portability. Choose 80mm+ for best low-light performance, or 50-60mm if weight is your biggest concern.
Can I use a spotting scope for stargazing?
Absolutely. A spotting scope with a large objective lens (80mm or more) and a zoom eyepiece can be a fantastic tool for viewing the moon, star clusters, and even some brighter planets. It’s more portable than many telescopes.
What’s more important, magnification or lens size?
They are equally important, but lens size often dictates overall image quality. A larger lens provides a brighter base image, which is then magnified. A good rule is to prioritize sufficient lens size for your lighting conditions first, then choose a sensible magnification range.