When it comes to stargazing and exploring the cosmos through a lens most people would probably call to mind the image of an astronomer’s telescope. These have their obvious benefits and we’ve outlined some of them in our post about the best telescopes for kids and starters. However, astronomy binoculars offer an affordable alternative that are not only cheaper but have the added benefit of being easily transportable and useful for day time use in all kinds of circumstances.
Some astronomers use astronomy binoculars in conjunction with their telescopes. They scan the night sky with the binoculars to find an object then use the telescope to examine it in more detail. These same binoculars might also be used at sporting events, concerts, or bird watching, but they need to be lightweight so that they are not cumbersome to use when swapping between telescope and binoculars.
All the below binoculars are best sellers on Amazon each with great reviews. Celestron are a brand leader in both telescopes and binoculars, as well as other optical instruments.
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Astronomy Binoculars Buyer’s Guide
It’s worth paying a little more for your astronomy binoculars because of the differences between the cheaper models that deliver views with blurry edges and the clearer, more accurate binoculars that minimise this image distortion. The better binoculars are those with lenses created with extra low dispersion (ED) glass. This type of glass is used in all kinds of optical instruments due to its ability to produce clearer images.
As well as the glass there is the prism type to consider. The consensus among stargazers is to choose astronomy binoculars containing a porros prism type as this kind of prism delivers more light from fainter celestial objects. For all other daylight use the roofer type prism is the norm as it is smaller and therefore allows for smaller and lighter binoculars.
Another factor to think about is the built quality of the binoculars. They are likely to be exposed to cold, moist air during the winter months. There is also a risk that they may be dropped or knocked during fieldwork, and we must also consider that since they are handheld devices pressed against the eyes, the look and feel of the materials used is a factor.
Magnification is another variable, but generally speaking the greater the magnification, the heavier the binoculars, so you’ll need to find a happy medium. Heavy binoculars can soon feel like a burden for tired arms but people vary so the right pair for you may be heavier or lighter than the pair suitable for anyone else.
The higher the magnification the more apparent is the shakiness you see when viewing objects. If your binoculars are too heavy for you and the magnification is on the high side then your view will be spoiled by the shaking. You could mount them on a tripod to overcome this, or simply buy a lighter pair with lower magnification.
Magnification is denoted by the first of the two numbers you’ll see in all the product descriptions. Thus 8 x 42 binoculars will magnify images to eight times what you can see with the naked eye. A magnification of up to 10 is most suitable for astronomy.
However, the second number denotes the diameter of the binocular’s lenses, and this is actually more important than the magnification. Lenses collect light from objects so the larger the lens, the more light they collect. The human eye’s lens diameter is about 6mm, so you can imagine how much more light a lens that 42mm can collect.
Thus 8 x 42 or 10 x 50 are suitable for low light conditions and sky watching. They are also useful for sailing when you might be looking into the distance under cloudy skies, or at dawn and dusk.
7 x 35 and 10 x 32 are best for daylight outdoor use (bird watching, camping etc), and 8 x 25 and 10 x 25 ten to be the lightweight set for general use at track and sporting events.
Field of View
Another point worth mentioning is the trade-off between magnification and field of view i.e. the total amount of sky you can see through the lenses. Higher magnification binoculars obviously help you to see more detail but they show a smaller field of view. This means it’s less easy to find objects in the night sky because you’re looking at less of it and you won’t see as many reference points that help locate an object.
It’s a bit like being too close to a location on Google Maps. You sometimes have to zoom out to see where it is in relation to more familiar landmarks.
The exit pupil is another measurement you’ll see mentioned with regard to binocular specifications This value is the result of dividing the lens diameter by the magnification, so a 7 x 35 pair will have an exit pupil measurement of 5mm (35 divided by 7).
Ideally this figure should be higher than 5mm. In dim light the human eye’s pupil can widen to 7mm, so if your binoculars can improve on that, so much the better. A 7 x 50 pair for example would give you a value of 7.14mm.
Relative brightness is a measurement related to exit pupil and is calculated by squaring the exit pupil value e.g. (7.14 x 7.14) equals 50.97. That is more than twice the relative brightness of a pair of binoculars with an exit pupil of 5mm – (5 x 5) equals 25.
Binocular eye relief is a measurement of the distance from the eyepieces to the eyes while the whole field of view is in view. The best option is a longer eye relief.
Field of view is usually denoted in feet and as previously mentioned this decreases with increased magnification.
Most binoculars have a central focus wheel but some may have what’s called a diopter adjustment ring on one of the barrels. This is designed to help those who need to compensate for differences between their two eyes.
Before you buy your first or next pair of astronomy binoculars, think about how you’re likely to use them. If you plan to have fixed in one place, perhaps even on their own tripod, then you could opt for a heavier pair. If on the other hand you will also use them on field trips, camping, sailing, or going to any sporting events, go for the lighter pair. Your neck and your arms will thank you for it.
Last update on 2022-01-28 / Affiliate links / Images from Amazon Product Advertising API