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How To Choose The Best Binoculars For Astronomy | Optics and Lab Equipment

How To Choose The Best Binoculars For Astronomy

Last Updated: 21.10.19


Some people might tell you that 10×50 binoculars are ideal for sky watching, while others will have a different opinion. What’s important to know is that you should stick to binoculars made for astronomy, and pick a pair that is powerful enough to help you reach the stars and that without leaving the planet Earth.

From specs to accessories, we will focus here on essential information that will help you pick a model that is right up your alley. Even if you are just a novice stargazer, you still need to learn a few things about what makes or breaks a good pair of binoculars for this purpose.



What magnification do you need?

The promise of high magnification often lures people who shop for a pair of binoculars for stargazing for the first time. This term describes how many times an image will be multiplied to bring the object closer to your eyes, and the temptation to choose a model with a lot of magnification is strong. After all, the stars are pretty far away, right.

However, you should know that it’s not practical at all to go for magnification that goes far above 10x. While this value may appear little to you, it is not ideal to hold a large pair of binoculars while you scout the night sky. The thing with high magnification is that it comes with a lot of image shakiness. Trying to hold the binoculars steady is too tricky and will tire your arms.

Of course, some models come with additional image stabilization features, but those are not cheap. The more state-of-the-art features a model has, the higher its cost, and that may not be exactly ideal for you and your budget.

Some people even advocate going as low as 7x or 8x magnification. Others say that 10x models are much better to observe the fine details of the celestial objects in the sky. There are definitely drawbacks to such a choice, as 10x binoculars offer a narrower field of view and more image shakiness.  


Don’t overlook the importance of the exit pupil size

While a lot of people focus on the debate regarding magnification, experts say that there is a correlated factor that many don’t even think about. They talk about the size of the exit pupil. That’s not something written clearly in the specs for a pair of binoculars, but you can calculate it by dividing the aperture by the magnification value.

To make things a bit clearer, for 7×50 binoculars, the size of the exit pupil is 7mm. For 10×50 models, this value is 5mm. As you can see, there are some differences to consider. But why is this measurement important?

This size should be a good match with the pupil of your eye. It is true that not everyone’s the same, and your eyes may not open as much as it happens for other people. Stargazers under 30 years of age have their pupils open to 7mm, while after that age, all people tend to lose 1mm of this value with each decade or more of their lives.

That may be an excellent argument to correlate your age with the type of binoculars you can use. The better fit you can obtain, the better, and for activities as demanding as sky watching, such aspects are particularly important.

Here is another thing to remember. If you choose a pair of binocular with high magnification, the exit pupil will be smaller compared to models with low magnification.


What role plays the prism design?

To learn what binoculars are truly a good fit for your needs, you must learn a little bit about optics. Let’s focus a little on the prism design and the role it plays when you shop around for a good pair to use for watching the night sky.

As you look at various models, you will observe a term that repeats for binoculars deemed appropriate for astronomy. That term is Porro prism, and it stands for the optical system inside the model that makes it possible for you to see a clear picture when you’re looking through the lenses of your binoculars.

Two Porro prisms should fit at correct angles so that they can fold and lengthen the light path. This is important for the user to see the correct image of what lies in front of him or her when using binoculars. They are installed a bit wider than the lenses, and they give binoculars that particular bumpy look.

There’s another, maybe unexpected benefit, to Porro prisms, such as the fact that binoculars fit better in your hands. Ergonomic design is a plus, so it’s a good thing that good optics meet comfortable design with so much ease.

You will also learn that there are models that come with roof prisms, and not Porro prisms. These binoculars tend to be more compact due to the particular design of their prisms. They are often preferred for the lightweight design, and also their cheap prices.

However, you should bear in mind that roof prism models can also be pretty expensive, and the chances are that the highest-priced binoculars you can find right now come outfitted with this type of optical design.



Some types of binoculars for astronomy

Even experts may agree that, as long as a pair of binoculars offers excellent performance, it would be a good fit for astronomy. Still, you should never overlook the fact that there are types of binoculars that fit better for such activities. They do come with some shortcomings, but it’s a good idea to learn a few things about them.

For instance, there are giant binoculars that will take your breath away from the first glance. As their name indicates, they are massive, and they may even compete with telescopes in terms of size. With apertures of up to 100mm, they will make an impression, but, as you can easily imagine, hiking them around and holding them can be a task you might not want to be burdened with.

Without a doubt, you should consider getting a tripod for such humongous binoculars. However, if you don’t intend to do a lot of stargazing, you might want to stick with some traditional 10×50 binoculars first.

You can also find binoculars with image stabilization on the market right now. These are pretty neat, and you won’t have to deal with the usual image shakiness that comes with the territory for high-magnification models.

There are not many negative things to say about such binoculars, except that they can be pretty costly. Not everyone can afford, so you may still want to stick with the recommended value from earlier.


Get a waterproof model

While the rule of thumb to keep the cost of a pair of binoculars down would be to forego any features that might hike up the price tag, some features are worth the money. Also, many manufacturers employ them even on low or medium entry models, so they are not that hard to come by.

We’re talking about waterproof models. You don’t have to go whale watching to need such a feature in your binoculars. Even air humidity can condense on the lenses and make it impossible to see clearly. Some models are waterproof, as well as fog proof, so they are the absolute winners.


A tripod adapter

Since you plan on watching the night sky and do so for hours, a tripod adapter is a good idea to have on a pair of binoculars designed for astronomy. Even if the manufacturer might not include the necessary tripod to help you get the best from your binoculars, it is a good idea to have one with an adapter.



Can you use such binoculars for terrestrial viewing?

Some of the models you can see on the market are versatile and can be used for other activities, besides examining the night sky. In case that’s something you want, you should search for features that are more important for terrestrial viewing.

A relatively decent close focus is a must, as models that are made for astronomy do not particularly excel in this field. Should you decide to take your binoculars for a trip to the great outdoors to watch birds, you will need a model with a small close focus.

Another thing is the total weight of the unit. You will surely want a model that won’t be too hard on your hands when you want to hold it for hours. 



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