Understanding Binocular and Spotting Scope Numbers
If you've ever picked up a pair of binoculars or looked at a spotting scope online, you’ve probably seen numbers like 8x42, 10x50, or 25–60x85 written in the specifications or on the product body. At first glance they can seem a bit technical, but they're actually very simple once you know what they mean.
These numbers tell you two key things: how much magnification you get, and how much light the optics can gather. Understanding them makes it much easier to choose the right binoculars or scope for birdwatching, wildlife observation, sports, hiking, or even astronomy.
What Do the Numbers Mean on Binoculars?
A binocular might be labelled 8x42. The first number, in this case 8x, refers to magnification. The second number, 42, refers to the size of the front objective lenses measured in millimetres.
So an 8x42 binocular means:
• the image appears 8 times closer
• the front lenses are 42mm wide
That's really all there is to it.
The magnification is the part most people notice first. If you are looking at a bird 800 metres away through 8x binoculars, it will appear roughly as though it is only 100 metres away. If you switch to 10x binoculars, it appears even closer.
At first, higher magnification sounds like it must always be better, but that's not necessarily true. Higher magnification gives you more detail at long distance, but it also makes the image shakier because every tiny movement of your hands becomes magnified too.
This is why many birdwatchers actually prefer 8x binoculars. They are steadier, easier to use, and give a wider view of the scene around you.
Why 8x42 Is So Popular
The 8x42 format has become something of a sweet spot in the optics world because it balances almost everything well. You get enough magnification for wildlife viewing, but not so much that the image becomes difficult to hold steady. The 42mm objective lenses also allow plenty of light into the binoculars, producing a bright and clear image in most conditions.
If you walk into a nature reserve, there’s a good chance a large percentage of visitors are carrying 8x42 binoculars.
By comparison, 10x42 binoculars give you more reach and detail, which can be useful in open landscapes or coastal areas where subjects are further away. The trade-off is a slightly narrower view and a little more image shake.
8 or 10x binoculars with 32mm objective lenses are also popular – for example 8x32. These type of binoculars are usually more compact and portable to carry – so if travelling light is a priority – then consider a 32mm. Remember the smaller the objective lenses – the less light reaches your eye.
Move up to something like 12x50 binoculars and you gain even more magnification and brightness, but they become noticeably larger and harder to hold steady for long periods. At that point many people start considering a tripod.
What Does the Objective Lens Size Do?
The second number, the 42 in 8x42, or the 50 in 10x50 tells you the diameter of the front lenses.
These lenses are called the objective lenses because they gather light before it travels through the binoculars to your eyes. In general, larger objective lenses collect more light, which produces a brighter image.
This becomes especially noticeable at dawn, dusk, or on cloudy days.
A compact pair of 8x25 binoculars might be excellent for travel because they are lightweight and easy to carry in a pocket or small bag, but they won’t perform as well in poor light as an 8x42 or 10x50.
On the other hand, very large lenses also make binoculars heavier and bulkier. That’s always the balancing act with optics, portability versus performance.
Understanding Field of View
Another specification you'll often see is field of view. This may be written as something like:
• 6.5°
• 120m at 1000m
• 340ft at 1000 yards
Field of view simply describes how wide an area you can see through the binoculars.
Imagine looking through a window. A wide window lets you see more of the landscape around you, while a narrow window zooms you in more tightly on one area. Binoculars work in a similar way.
Lower magnification binoculars usually have a wider field of view. This makes them excellent for tracking birds in flight or following moving wildlife because it is easier to keep the subject in sight.
Higher magnification binoculars typically have a narrower field of view. You see more detail, but less of the surrounding scene.
This is one reason why beginners often find 8x binoculars easier to use than 12x models. The wider field makes it much simpler to locate subjects quickly.
Spotting Scope Numbers Explained
Spotting scopes use similar principles, but their numbers look slightly different because most scopes have variable zoom eyepieces.
You might see a spotting scope labelled 25–60x85.
The 25–60x means the magnification is adjustable. At the low end, the eyepeice of the scope magnifies 25 times. At the high end, it magnifies 60 times.
The 85 refers to the diameter of the main front lens, again measured in millimetres.
So a 25–60x88 spotting scope is a scope with:
• Adjustable magnification eyepeice between 25x and 60x
• An 88mm objective lens
Why Spotting Scopes Use Zoom Magnification
Unlike binoculars, spotting scopes are usually designed for very long-distance observation. You might use one to watch coastal birds, scan hillsides for wildlife, observe ships offshore, or even view targets at a shooting range.
At lower magnifications, around 20x to 30x, the image is brighter, wider, and easier to use. This is often the best range for general viewing. As you increase magnification toward 40x, 50x, or 60x, you start seeing much finer detail. Feathers, markings, or distant objects become clearer. However, there are trade-offs. The image becomes dimmer, the field of view narrows, and atmospheric conditions begin to affect image quality more noticeably. Heat haze on a warm day, for example, can make a highly magnified image appear soft or wavy. This is why experienced users often say that maximum magnification is not always the most useful setting.
Why Large Objective Lenses Matter More on Scopes
Large objective lenses become especially important on spotting scopes because high magnification naturally reduces brightness.
A small 50mm spotting scope at 60x magnification can look relatively dim, especially in poor light. An 85mm scope at the same magnification will usually appear brighter and sharper because it gathers more light. That's why serious birdwatchers and wildlife observers often favour scopes in the 80mm to 99mm range despite the extra size and weight. Of course, portability matters too. A smaller 60mm scope is much easier to carry on long hikes or while travelling, even if it sacrifices some low-light performance.
Choosing the Right Option
The best optics are not necessarily the most powerful ones. The right choice depends on how you plan to use them.
For general birdwatching and everyday outdoor use, 8x42 binoculars are often considered the ideal all-round option because they are bright, steady, and easy to use.
If you regularly observe wildlife over long distances, 10x42 or 10x50 binoculars may suit you better.
If you really want to travel light then consider an 8x32 binocular. For hiking you might even consider a pocket 25mm binocular.
For serious long-range observation, especially from fixed locations, a spotting scope such as a 25–60x88 offers far more detail than binoculars ever can, although it requires a tripod to keep the view stable.
In the end, all of these numbers are really about balancing four things:
• magnification
• brightness
• field of view
• portability
Once you understand what the numbers mean, choosing binoculars or a spotting scope becomes much less intimidating and much more enjoyable.
Best binoculars to start with:
Best beginner scope:
