10×50 vs 8×42 – Binocular numbers explained in simple terms

Binoculars are similar to telescopes in the sense that most people have no idea what the numbers mean and what they even refer to. The truth is that if you don’t know what these numbers mean, then you can’t really consider getting a set of astronomy binoculars for yourself. Like a telescope has its focal length and aperture, you need to know what the numbers on your binoculars mean too.

So, I’m going to try and explain things as simply as possible. It’s actually pretty easy to understand, but long scientific words can make things confusing. So, I’ll be using simple English to convey what these numbers mean, and how they’ll affect your viewing experience.

10×50 vs 8×42 – Binocular numbers explained

When it comes to binoculars, you have two key numbers to remember. In the example 10×50, the ten refers to the magnification of your pair of binoculars. The fifty refers to the diameter of the objective lens of your binoculars – that’s literally the two lenses you look through when you’re using your binoculars.

So, magnification is the first number, and the objective lens size is the second number. Simple. But how do these numbers make a difference when you’re actually using your binoculars? That’s the important part.

Binocular magnification

The first number of the two refers to the magnification of your binoculars. In a common pair of binoculars, you’re going to see typical magnifications of 8x and 10x. Any less than this and they’re likely to be used for other purposes, like watching sports or whale watching.

The largest magnification you can usually have in a pair of handheld binoculars is around 12-14x. When we go any more magnified than this, it can be very difficult to see the image clearly, as your hands are never really completely still. That’s why when you see 20x magnification binoculars, you’re going to want to use a mount or tripod with them for best effect.

So, the magnification is literally just the times closer that the object you’re looking at will appear to you. The higher the magnification, the greater detail you’ll be able to see night sky objects in. The downside of this is that you sacrifice some field of view, which means you’re going to get a narrower view of the sky.

It really depends on what you’re looking for. Most people use a pair of binoculars as an accompaniment to their telescope, not instead of. For this, 8-10x will be just fine for getting a good view of the surrounding sky.

Objective Lens

Whilst the first number in your binoculars is very important, so is the second number. It refers to the diameter of the objective lens of your binoculars, which is literally the size of looking lens.


The greater the size of your objective lens, the more light it can gather – it’s the equivalent of the aperture of your telescope. What does this mean for the view that you’ll get through your binoculars? Well, more light gathered will allow you to see things in much greater detail. Not only this, but the objects you look at through the lens will be much sharper and brighter due to the increased light.

The downside of increasing the size of your objective lens is obviously, it’ll increase the size of your binoculars at the same time. This is why most full size binoculars are limited to 42 or 50mm, as they become larger and more difficult to cary when you go larger than that.

At the other end of the spectrum, you can also get smaller binoculars with smaller objective lenses. A standard set of super compact binoculars may only have 30mm objective lenses. You’ll be able to carry them with you much easier,

How can two sets of 10×42 be drastically different in price?

Another one of the most common questions I get about binoculars are how two binoculars that are the same specs (magnification + objective lens) be completely different prices. You can easily pick up a set of binoculars with these specs for less than $50, and you can just as easily spend $1000+ on a pair that state they have the same “power”.

The real difference between them will come in the quality of the parts that make up your pair of binoculars. One of the most common reasons that a pair may be more expensive is the prism type that they use. A set of roof prism binoculars will often cost more than a porro prism set, as there are benefits to their build.

But it’s not only the prism type that you need to take into account here. You’re also going to want to think about the quality of the optical lenses used and the coatings that are added to them. Generally, the quality of the parts used are going to b the main factor in how much a set of binoculars cost you, not the magnification.


It’s really important to understand the key factors to consider when you’re buying a pair of binoculars. The magnification is very important, as it’s going to be the difference between you viewing the moon in detail or not. Typically no matter the magnification, a telescope will be better if you’re looking to view planets up close. Go for a smaller objective lens if you want something compact to carry around with you, and a larger one if you want to see more detail (bearing in mind they’ll be bigger and heavier to carry).

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