Astronomical binoculars : A guide to astronomy with binoculars

by: OZScopes - The Australian Telescope Experts

Want to see nebulae with astronomical binoculars?

Want to see nebulae with astronomical binoculars?

A good pair of binoculars - with the right specifications - will be a great stand-in for a telescope. This guide will provide you with a quick take on a buying guide for astronomical binoculars, as well as provide a quick review of astronomy binoculars.

Binoculars are a great option for those who aren't interested in the complexities, size or price of a telescope, and they will still allow you observe the moon and stars, nebulae, and even Jupiter and its moons. Furthermore, binoculars allow you to use both eyes for a more three-dimensional, "stereo" visual experience.

As with telescopes, a critical feature for astronomy binoculars is the size of the objective lens, otherwise known as the aperture.

Aperture is a term that refers the the diameter of the objective lens (the main lens/mirror) used in optical equipment. Generally, the larger the aperture, the better the image quality of the telescope/binoculars - but, it directly correlates to the weight of the item as well (i.e. the larger the aperture, the heavier the item). Image quality improves with larger aperture sizes because the lenses are able to better capture light, providing you with a brighter, clearer and more vibrant image.

So how do I find the aperture size of a pair of a pair of binoculars?

Generally, all binoculars have a common way of stating their specifications in their name. For example, with the Celestron SkyMaster 25x100 Binoculars (Which are, incidentally, really good binoculars for astronomy, by the way), you'll notice that there are some numbers in the title. Those are the specifications of the pair, and they are read like this:

a) Magnification/Power : the power or magnification of your binoculars can be found in the first set of numbers in it specifications. In this case, it's an 25x (fixed) magnification.

b) Aperture : The aperture, or the size of the objective lens, can be found in the last set of numbers. Always read in mm, this pair has a 100mm aperture, which is nice and big for astronomical use.

In the event that a pair of binoculars has more numbers in its specification, such as the Celestron SkyMaster 20-100x70 Zoom Binoculars, the same rule applies. The Magnification/Power of the pair ranges from 20x - 100x, which is what's known as a variable zoom. A variable zoom simply means that you're able to zoom in and out on objects, much like you would with a standard point-and-shoot camera. For more information on binoculars, read our guide to binocular basics here.

What aperture size is good for astronomy?

We now understand that aperture is the key factor to determining clarity and brightness. Typically, industry recommends a minimum of a 50mm aperture size to be able to view celestial object properly. As astronomy (obviously) takes place at night, the ability to capture light could not be more important. A large aperture size allows your binoculars to capture more light, thus allowing you to see fainter objects in the sky that would otherwise be invisible to you. Known as night binoculars, manufacturers sometimes make binoculars that have been optimized for astronomical use. You'll be able to see OZScopes's collection of night binoculars here. We recommend you guys have a look at the:

a) Celestron SkyMaster 15x70 Binoculars - 15x magnification, 70mm aperture (Our most popular pair of astronomy binoculars!)

b) Celestron SkyMaster 20x80 Binoculars - 20x magnification, 80mm aperture

c) Barska X-Trail 20x80 Binoculars - 20x magnification, 80mm aperture (Really bright and clear images at an affordable price point.)

What about magnification, then?

The ideal magnification or power for astronomical binoculars vary. When using binoculars for astronomy, the quality of the image doesn't really relate to very high powers or magnifications. For example, you will get a better viewing experience with a pair of 20x80 binoculars than with a 30x80 pair, despite the reduced magnification. Why?

a) Firstly, you'll get a wider field of view with the 20x80 than with the 30x80 - astronomy binoculars were engineered to look at a range of objects rather than specific planets (which is more a telescope's job).

b) Secondly, the exit pupil of the 30x80 will be smaller than the 20x80, which will result in a darker, less clear image.
To calculate the Exit Pupil of a pair of binoculars, simply divide the aperture (diameter of the objective lens) with the magnification (power). The result is the exit pupil in mm. OzScopesrecommends that the minimum exit pupil for good astronomical viewing is 4mm.

How portable are night binoculars?

While night binoculars are as portable as the next pair, they are significantly heavier due to their larger objective lenses (aperture). This makes them less ideal for holding up to your eyes for extended periods of time. They're generally pretty hefty, weighing roughly 1.3kg at the lightest. Most people find it convenience to purchase a tripod for their night binoculars, and you'll be able to find our range of tripods here. We recommend the:

a) SAXON HVT11 Heavy Duty Tripod for Binoculars, Cameras and Spotting Scopes

- Able to extend to 1850mm in height, it's a really convenient, heavy-duty tripod with smooth control and functionality.

b) SAXON HVT10 Heavy Duty Tripod for Binoculars, Cameras and Spotting Scopes

- Able to extend to 1650mm, you might have to duck slightly when using this tripod for astronomy, but it's really good value and sturdily built.

All binoculars (astronomical ones or otherwise) or adaptable to tripods. Read our product descriptions to see if the binoculars you're after come with a tripod adapter. If they don't, you can purchase a Saxon Tripod Adaptor for Binoculars to allow your binoculars to attach to any standard tripod. Be aware though the Saxon tripod adapter will take the weight of binoculars up to 100mm in aperture size. Any bigger than that and the tripod adapter might snap.

Keeping It Steady

One of the greatest challenges you'll find when using binoculars to stargaze will be to hold them steady. Like mentioned previously, you're probably best to go with a tripod, but find below some alternatives for free-standing binocular stargazing!

1. Use lower powers. Although most people can quite comfotably hold 7x or 8x binoculars steady, it starts to become difficult to keep 10x binos steady for an extended period of time. If your binoculars are more powerful than that, you're going to experience some difficulty holding it steady without a dedicated mount.

2. Try to lean against something. Whether it's a tree, a car, or even a wall, you'll find that leaning on something solid will result in your images becoming steadier.

3. Planning on sitting? Relax in a lawn chair. The best will be the sort that reclines all the way - 180 degrees. With your back and elbows supported, you'll find your views get steadier and sharper. If you use a chair without back support, be sure not to tip over when staring overhead! Lying on the ground will also be helpful.

4. Some amateur astronomers report some success by holding the end of the left barrel with the right hand, and letting the right barrel rest on the wrist, and then pushing them gently against your face. This creates a sturdier, more rigid way of holding the binos closer to the eyepieces.end of the left barrel with the right hand, and letting the right barrel rest on the wrist, and then pushing them gently against the head 5. Check the internet. There are some pretty cool DIY (do-it-yourself) binocular-mount projects online, such as with a simple broomstick!

Happy hunting!

Good luck with stargazing, astronomers! To aid you with your search in the stars, there are a number of items to make things easier for you.

A planisphere - or star disc - is very helpful to tell you what's visible in your sky on any given date during the year. Our Star Disc has been optimized for the Southern Hemisphere, and shows you what's visible in Australian skies (and New Zealand, South America, South Africa, etc.). You'll be able to find Star Charts, Moon Phase Maps (with CD!) and other visual aids for astronomy here.