How To Choose Binoculars For Astronomy

Many think that only a beginner would use binoculars for stargazing instead of a telescope, which is not true. I have been an amateur astronomer for over thirty years, and I still often use binoculars.

Indeed, some use binoculars to help them find objects before looking at them closer with a telescope. However, there are some celestial objects that are better seen with binoculars.

One of the advantages of binoculars is that they are very good at catching faint light over a wide field to view objects such as nebulas, star clusters, galaxies, and our own Milky Way.

So, I believe that binoculars are a useful tool for stargazing on par with a telescope, although I admit that their areas of specialty are quite different.

Therefore, I suggest that you choose binoculars as your first tool when starting out as a stargazer. A good pair will be useful for a long time.

In this post, I will tell you how to go about choosing good binoculars for astronomy.

Are binoculars better than telescopes for beginners?

Looking back on my early days, I’m convinced that beginners should start with binoculars for stargazing.

Fascinated with astronomy, I begged my father to buy me a nice telescope, which was too expensive for a child. He decided to wait until I got bored with the idea, but I never did! I would have done anything to have a telescope.

One day, I found some old binoculars in the closet, which I didn’t take too seriously. I soon realized that they worked much better than my naked eyes.

I could clearly see some large craters on the moon, Galilean moons around Jupiter, and some of the brightest nebulas and star clouds.

Within six months, I had seen most of the celestial objects that can be seen with binoculars.
I still craved a telescope to take a closer look at the smaller craters on the moon, clouds bands on Jupiter, and the rings of Saturn.

After begging my father for another six months, he finally bought me a telescope!

The telescope enabled me to see objects in closer detail, but I still needed my binoculars for stargazing.

Binoculars take no time to prepare and help me locate objects quickly before looking at them through my telescope.

I really appreciate my father making me wait a year before getting me a telescope. It gave me time to get more enthusiastic about astronomy. Thanks to the binoculars, I gained valuable knowledge of astronomy before I got my telescope.

In conclusion, beginners should start with binoculars, not a telescope.

Binoculars have many uses besides stargazing, so they will never be collecting dust just in case you lose your interest in astronomy.

How to choose binoculars for astronomy

While some binoculars are great for stargazing, not every pair will do the job.  Some are good for astronomy, and others are not.  What matters most for stargazing is brightness.

Your pupils control how much light gets into your eyes.

At night, our pupils dilate to allow more light in so that we can see dark objects clearly.  In the sunlight, our pupils shrink to restrict the amount of bright light.

When you look at stars at night, our pupils are open wide.  How wide our pupils open depends on one’s age.  Young people can dilate their pupils to about 7.5mm while middle-aged people (like me) can open them to about 5mm.

If you use binoculars with smaller exit pupils than your pupil size, the binoculars won’t feel bright enough.

For this reason, young people need binoculars with exit pupils from 5mm to 7mm, and middle-aged people, from 4mm to 6mm.

The aperture is essential.

The amount of light that makes it to your eyes is proportional to the square of the aperture. You need binoculars with large objective lenses to see as many stars as possible.

However, large binoculars made for astronomical use have to be mounted on a tripod, which causes another problem.

A tripod with binoculars means you are not as mobile anymore. The thought of a heavy tripod with binoculars might prevent you from wanting to stargaze.

Furthermore, since you need to bend your neck upward, it becomes painful to look at stars at the zenith (directly above).

For beginner stargazers, I think 50×7 or 42×8 binoculars are easiest to handle. 50×7 have a 7mm exit pupil, and 42×8 have a 5.3mm exit pupil, both of which will give you sufficient brightness.

If you want to look at objects at the zenith, a foldable reclining chair is recommended as it is much more comfortable.

Sharpness

When I test binoculars, I look for fourth-magnitude stars. Higher magnitude stars (1-3) are too bright to demonstrate how sharp your binoculars are.

Stars are far away from earth, so they look like pinpoints. They twinkle because of the atmosphere.

With sharp binoculars, I can see a pinpoint image in the center; though they get blurry as they get closer to the peripheral area of view (see below).

If your binoculars have a clear vision in 30% of the whole image circle, the pair is good enough, because you usually put what you want to see in the center.

Some excellent binoculars, such as the Fujinon 7×50 FMT-SX2, have field flattener lenses to get incredibly sharp images throughout the entire view.

Waterproof

You may experience night dew while you are stargazing. I’m sometimes surprised when I notice my binoculars are covered with dew droplets.

It’s worth buying a waterproof pair to protect them from night dew.

Nitrogen gas-filled binoculars prevent them from fogging on the inside of the lenses, which is effective in preventing fungus growth.

There are a few disadvantages to waterproof binoculars. They say that waterproof binoculars are only good for ten years because the O-rings deteriorate.

Also, waterproof binoculars are a little heavier than non-waterproof, and they cost more.  However, considering the risks of getting wet or fogging up, it’s worth it to buy a waterproof pair.

Are 7×50 and 10×50 the best choices?

In my childhood, 7×50 binoculars were said to be the standard for stargazing. There was no choice.

Indeed, they have large objective lenses with a 7mm exit pupil.  However, these days, some people disagree with this standard.

Some recommend 8×42 instead of 7×50 or 10×50 for the following two reasons.

First, as coating technology improves, a 42mm aperture can collect as much light as an old pair with 50mm.

Second, as city lights have polluted the night sky, a 7mm exit pupil is excessive. With 7×50, dim stars can blend in with the background too easily.

For example, I like looking at the Double Cluster in Perseus with binoculars. The Double Cluster against a background of the galaxy can fit into the same image circle with my binoculars. This takes my breath away.

If I use 7×50 under truly dark skies, I have no problem.

However, in the countryside-suburban areas, the sky is slightly light-polluted, which lowers the contrast of stars and the background.

With a 5mm or 4mm exit pupil, you’ll be able to see those stars against a dark sky.

Considering only the exit pupil, 10×50 seems best. However, 10× magnification causes ‘image shake.’

Binoculars magnify the tiny motions your hands make while stargazing.  So, I prefer 8× or lower, rather than 8× to 10×.

In conclusion, deciding whether to choose 7×50 or 8×42 can depend on your observing location.

If you can see sixth-magnitude stars on a moonless night with your naked eyes, do not hesitate to choose 7×50.

However, if you are middle-aged, and have few occasions to go stargazing without light pollution, I suggest that you buy 8×42.

I have been using 8×42 for astronomy since I turned 40, and I don’t feel like it’s a compromise.

Special binoculars for stargazing: large binoculars and an image stabilizer

If you are looking for a second pair of binoculars specifically for astronomy, I recommend you to consider two different types.

• Large binoculars for stargazing

If your binoculars’ aperture is over 70mm, they can be considered ‘Astronomy Binoculars.’  They are too heavy to hold in your hands. They need to be mounted on a tripod.

These types of binoculars are the best for astronomy.  It feels comfortable and natural to see stars with both eyes open (unlike most telescopes).

In contrast to regular binoculars, the objective lenses can collect as much light as telescopes with a higher magnification. A typical combination is 15×70 or 20×80.

With astronomy binoculars, the number of nebulas and star clusters you can enjoy increases twofold.

One of the disadvantages of astronomy binoculars is the weight (over 2kg) which requires a tripod. Because of this, you lose mobility.

Again, astronomy binoculars can be good as a second pair. Those just starting out should consider ones that are not built specifically for astronomy as their first pair.

The best image stabilized binoculars: Canon 10×42 L IS

No matter what binoculars you choose, you will encounter ‘image shake’ in varying degrees, except with one type: image-stabilized binoculars.

I strongly believe that the Canon 10×42 L IS are the best of the best. Without the image stabilizer, this pair produces a super sharp image.  Once you turn on the image stabilizer, the impact is so great that it will give you goosebumps!

When I first used a pair to look at the Beehive Cluster (M44), also known as Praesepe, I did not turn on the stabilizer.  I could clearly see the cluster and could make out some of the dim stars.

Holding the binoculars still with the cluster in the center of view, I turned on the stabilizer.  Suddenly, so many dim stars appeared as the view stabilized.

This effect stunned me so much that I started aiming at other objects, one after another.

The great advantage of image-stabilized binoculars is that you do not need a tripod, which enables you to look at the sky without straining your neck.

Lying on a reclining chair with the stabilized-binoculars feels so comfortable that you can enjoy stargazing for hours.

What do they look like with binoculars?

Perhaps beginners cannot imagine what celestial objects look like through binoculars.

Astronomical photographs are beautiful, but they are not the same as what you can see through binoculars.

In this part, I will describe what the objects look like through binoculars. I encourage you to get binoculars so you can look at these objects for yourself.

The moon and the planets: Saturn and Jupiter

The moon is one of the most remarkable objects to look at because it has a lot of craters and details on the surface.  If you want to see them clearly, choose a night when you can see a half-moon.

When sunlight shines the moon from the side, it makes long shadows on the surface.  Even with compact binoculars, you can find amazing details and shadows near the line of lunar day and night.

Looking at the crescent moon, you can find the earthshine casts a dim light over the dark side of the moon, which is very beautiful.

The full moon has no shadows, which means you cannot see craters in 3 dimensions. The image is flatter.

I still like looking at the full moon with binoculars.  It looks like a big disk floating in the sky.

• The Planets

Venus, known as the evening star, is easy to find, but with binoculars, it is too bright.

If you want to see the shape of Venus, try to find it in the daylight.  Venus looks like a small half-moon in the blue sky.

Please be careful not to look at the sun with binoculars.

Jupiter is my favorite planet to look at.  It has four large moons, the so-called Galilean Moons, which you can easily find with binoculars.

Sorry to say, you cannot see the stripes of Jupiter because of the low magnification.

Mars and Saturn are not so interesting as they appear too small.  You will find that Saturn has more area than other stars, but you will not be able to see the rings.

If you want to enjoy these planets, you’ll need a large telescope with high magnification.

Andromeda Galaxy and the Orion Nebula

Binoculars show their advantage most when you look at large nebulas and star clouds.  However, their clarity depends greatly on sky conditions.

A dark, moonless, and clear sky is the best way to enjoy nebulas and star clouds.

Unlike the planets, it is much more challenging to locate these objects with so many stars in the background, because they are so dim. When you do locate them, they can be stunning, which is the real pleasure of stargazing.

Andromeda Galaxy, M31, and Orion Nebula, M42, are musts for binocular users.

I’ll never forget the image of the Andromeda Galaxy with Nikon’s 10×70 in my early twenties.  I felt as if I were in a spaceship looking at it through the round window.

After looking up at it for an hour, I got a crick in my neck!

In the northern hemisphere, the Orion Nebula or M42 appears in winter.  Even beginners can find this nebula without any difficulty since it is in the famous constellation of Orion.

With binoculars, it looks like a small bluish bird flying in the sky.  In the middle of it, there is a trapezium cluster consisting of four stars.

I once tried to take a closer look at this trapezoid to test the clarity of my Zeiss 7×42.  I could barely make out the four stars individually.

A lunar eclipse and a solar eclipse

Total lunar eclipses are more common than total solar eclipses.

For viewing lunar eclipses, binoculars are much more useful than telescopes.

When the moon passes completely through the Earth’s shadow, you get a total lunar eclipse. During the total eclipse, the moon appears red with many stars in the background.

In Japan, people enjoy lunar eclipses, comparing them to a paper lantern floating in the sky. Even with compact binoculars, you will be astonished by the beautiful red moon.

• A total solar eclipse

In 2017, I envied those in the U.S., because they witnessed a total solar eclipse across their mainland. I’m sure many people were fascinated with the phenomena.

I saw a total solar eclipse in Iran in 1999. I took my large 25×100 binoculars with a tripod to see it.

With my naked eyes, I could see the moon ringed by the pearly white corona in a twilight sky. With my binoculars, I was overwhelmed by the unbelievably spectacular view of the solar corona.

The corona looked like shining myriad silk threads. On the rim of the black moon, I could see coronal prominence erupting from the sun. Carrying heavy binoculars all the way to Iran really paid off with that sight.

You do not need large binoculars to enjoy a total solar eclipse. 7×50 or 8×42 will do.

One more thing: it is never safe to look at the sun through binoculars during the partial phases of an eclipse.  If you let children use binoculars for a total solar eclipse, please be careful.

Summary

If you are new to stargazing, and even if you can afford to buy a decent telescope, you should wait. As a first step, I recommend you search your closets for binoculars or buy a good pair for astronomy.

With binoculars, you can learn a lot about astronomy which is useful when you buy a telescope in the future. More importantly, binoculars are better than telescopes at seeing some objects such as nebulas and star clusters.

To get a better image even with a dark sky, you should choose binoculars with a large exit pupil and large objective lenses. Typical binoculars for astronomy used to be 7×50 or 10×50, but as coating technology improves, 8×42 is also a good choice.

When choosing a second pair of binoculars for stargazing, you should keep large binoculars and image-stabilized binoculars in mind. Compared to regular binoculars, astronomy binoculars are so powerful that you can enjoy many more objects and an image stabilizer enables us to be free of ‘image shake.’

Stargazing with binoculars and a star map is a lot of fun. When you have a chance to see astronomical phenomena such as a total lunar eclipse, a total solar eclipse, and comets, binoculars can be a powerful tool to observe them.

I want to stress again that beginner stargazers should start with binoculars, not telescopes.