Binoculars for Astronomy
Written by Tammy Plotner
Astronomy is best when you get outside and look into the skies with your own eyes. And the best way to get started is with a set of binoculars for astronomy. They're light, durable, easy to use, and allow you to see objects in the night sky that you just couldn't see with your own eyes. There are so many kinds of binoculars out there, so we've put together this comprehensive guide to help you out.
Everyone should own a pair of binoculars. Whether you're interested in practicing serious binocular astronomy or just want a casual cosmic close-up, these portable "twin telescopes" are both convenient and affordable. Learning more about how binoculars work and what type of binoculars work best for astronomy applications will make you much happier with your selection. The best thing to do is start by learning some binocular "basics".
What are binoculars and how do they work?
Binoculars are both technical and simple at the same time. They consist of an objective lens (the large lens at the far end of the binocular), the ocular lens (the eyepiece) and a prism (a light reflecting, triangular sectioned block of glass with polished edges).
The prism folds the light path and allows the body to be far shorter than a telescope. It also flips the image around so it doesn't look upside-down. The traditional Z-shaped porro prism design is well suited to astronomy and consists of two joined right-angled prisms which reflects the light path 3 times. The sleeker, straight barrelled roof prism models are more compact and far more technical. The light path is longer, folding 4 times and requires stringent manufacturing quality to equal the performance. These models are better suited to terrestrial subjects, and are strongly not recommended for astronomy use.
If you're using binoculars for astronomy, go with a porro prism design.
Choosing the Lens Size
Every pair of binoculars will have a pair of numbers associated with it: the magnifying power times (X) the objective lens size. For example, a popular ratio is 7X35. For astronomical applications, these two numbers play an important role in determining the exit pupil – the amount of light the human eye can accept (5-7mm depending on age from older to younger). By dividing the objective lens (or aperture) size by the magnifying power you can determine a pair of binoculars exit pupil.
Like a telescope, the larger the aperture, the more light gathering power – increasing proportionately in bulk and weight. Stereoscopic views of the night sky through big binoculars is an incredible, dimensional experience and one quite worthy of a mount and tripod! As you journey through the binocular department, go armed with the knowledge of how to choose your binoculars lens size.
Why does the binocular lens size matter? Because binoculars truly are a twin set of refracting telescopes, the size of the objective (or primary) lens is referred to as the aperture. Just as with a telescope, the aperture is the light gathering source and this plays a key role in the applications binoculars are suited for. Theoretically, more aperture means brighter and better resolved images – yet the size and bulk increases proportionately. To be happiest with your choice, you must ask yourself what you'll be viewing most often with your new binoculars. Let's take a look at some general uses for astronomy binoculars by their aperture.
Different Sizes of Binoculars
Binoculars with a lens size of less that 30mm, such as 5X25 or 5X30, are small and very portable. The compact models can fit easily into a pocket or backpack and are very convenient for a quick look at well-lit situations. In this size range, low magnifications are necessary to keep the image bright.
Compact models are also great binoculars for very small children. If you're interested in choosing binoculars for a child, any of these models are very acceptable – just keep in mind a few considerations. Children are naturally curious, so limiting them to only small binoculars may take away some of the joy of learning. After all, imagine the thrill of watching a raccoon in its natural habitat at sundown… Or following a comet! Choose binoculars for a child by the size they can handle, whether the model will fold correctly to fit their interpupilary size, and durability. Older children are quite capable of using adult-sized models and are naturals with tripod and monopod arrangements. For less than the price of most toys, you can put a set of quality optics into their hands and open the door to learning. Children as young as 3 or 4 years old can handle 5X30 models easily and enjoy wildlife and stargazing both!
Binocular aperture of up to 40mm is a great mid-range size that can be used by almost everyone for multiple applications. In this range, higher magnification becomes a little more practical. For those who enjoy stargazing, this is an entry level aperture that is very acceptable to study the Moon and brighter deep sky objects and they make wonderful binoculars for older children.
Binoculars up to 50-60mm in lens size are also considered mid-range, but far heavier. Again, increasing the objective lens size means brighter images in low light situations – but these models are a bit more bulky. They are very well suited to astronomy, but the larger models may require a support (tripod, monopod, car window mount) for extended viewing. Capable of much higher magnification, these larger binocular models will seriously help to pick up distant, dimmer subjects such as views of distant nebulae, galaxies and star clusters. The 50mm size is fantastic for older children who are ready for more expensive optics, but there are drawbacks.
The 50-60mm binoculars are pushing the maximum amount of weight that can be held comfortably by the user without assistance, but don't rule them out. Available in a wide range of magnifications, these models are for serious study and will give crisp, bright images. Delicate star clusters, bright galaxies, the Moon and planets are easily distinguishable in this aperture size. These models make for great "leave in the car" telescopes so you always have optics at hand. For teens who are interested in astronomy, binoculars make an incredible "First Telescope". Considering a model in this size will allow for most types of astronomical viewing and with care will last through a lifetime of use.
Binoculars any larger than 50-60mm are some serious aperture. These are the perfect size allowing for bright images at high magnification. For astronomy applications, binoculars with equations like 15X70 or 20X80 are definitely going to open a whole new vista to your observing nights. The wide field of view allows for a panoramic look at the heavens, including extended comet tails, large open clusters such as Collinder Objects, starry fields around galaxies, nebulae and more… If you have never experienced binocular astronomy, you'll be thrilled at how easy objects are to locate and the speed and comfort at which you can observe. A whole new experience is waiting for you!
Binocular Magnification
When choosing binoculars for astronomy, just keep in mind that all binoculars are expressed in two equations – the magnifying power X the objective lens size. So far we have only looked at the objective lens size. Like a telescope, the larger the aperture, the more light gathering power – increasing proportionately in bulk and weight. Stereoscopic views of the night sky through big binoculars is an incredible, dimensional experience, but for astronomical applications we need these two numbers to play an important role in determining the exit pupil – the amount of light the human eye can accept. By dividing the objective lens (or aperture) size by the magnifying power you can determine a pair of binoculars exit pupil. Let's take a look at why that's important.
How do binoculars magnify? What's the best magnification to use? What magnifying power do I choose for astronomy? Where do I learn about what magnifying power is best in binoculars? Because binoculars are a set of twin refracting telescopes meant to be used by both eyes simultaneously, we need to understand how our eyes function. All human eyes are unique, so we need to take a few things into consideration when looking at the astronomy binocular magnification equation.
By dividing the objective lens (or aperture) size by the magnifying power you can determine a pair of binoculars exit pupil and match it to your eyes. During the daylight, the human eye has about 2mm of exit pupil – which makes high magnification practical. In low light or stargazing, the exit pupil needs to be more around 5 to be usable.
While it would be tempting to use as much magnification as possible, all binoculars (and the human eye) have practical limits. You must consider eye relief – the amount of distance your eye must be away from the secondary lens to achieve focus. Many high "powered" binoculars do not have enough outward travel for eye glass wearers to come to focus without your glasses. Anything less than 9mm eye relief will make for some very uncomfortable viewing. If you wear eyeglasses to correct astigmatism, you may wish to leave your glasses on while using binoculars, so look for models which carry about 15mm eye relief.
Now, let's talk about what you see! If you look through binoculars of two widely different magnifying powers at the same object, you'll see you have the choice of a small, bright, crisp image or a big, blurry, dimmer image – but why? Binoculars can only gather a fixed amount of light determined by their aperture (lens size). When using high magnification, you're only spreading the same light over a larger area and even the best binoculars can only deliver a certain amount of detail. Being able to steady the view also plays a critical role. At maximum magnification, any movement will be exaggerated in the viewing field. For example, seeing craters on the Moon is a tremendous experience – if only you could hold the view still long enough to identify which one it is! Magnification also decreases the amount of light that reaches the eye. For these reasons, we must consider the next step – choosing the binocular magnification – carefully.
Binoculars with 7X magnifying power or less, such as 7X35, not only delivers long eye relief, but also allows for variable eye relief that is customizable to the user's own eyes and eyeglasses. Better models have a central focus mechanism with a right eye diopter control to correct for normal right/left eye vision imbalance. This magnification range is great for most astronomy applications. Low power means less "shake" is noticed. Binoculars with 8X or 9X magnification also offer long eye relief, and allows comfort for eyeglass wearers as well as those with uncorrected vision. With just a bit more magnification, they compliment astronomy. Binoculars with 10X magnifying power are a category of their own. They are at the edge of multipurpose eye relief and magnifying power at this level is excellent across all subject matter. However, larger aperture is recommended for locating faint astronomy subjects.
Binoculars with 12-15X magnifying power offer almost telescopic views. In astronomy applications, aperture with high magnification is a must to deliver bright images. Some models are extremely well suited to binocular astronomy with a generous exit pupil and aperture combined. Binoculars with 16X magnification and higher are on the outside edge of high magnification at hand-held capabilities. They are truly designed exclusively as mounted astronomical binoculars. Most have excellent eye relief, but when combined with aperture size, a tripod or monopod is suggested for steady viewing. If you're interested in varying the power, you might want to consider zoom binoculars. These allow for a variety of applications that aren't dependent solely on a single feature. Models can range anywhere from as low as 5X magnification up to 30X, but always bear in mind the higher the magnification – the dimmer the image. Large aperture would make for great astronomy applications when a quick, more magnified view is desired without being chained to a tripod.
Other Binocular Features
The next thing to do is take a good look at the binoculars you are about to purchase. Check out the lenses in the light. Do you see blue, green, or red? Almost binoculars have anti-reflection coatings on their air to glass surfaces, but not all are created equal. Coatings on binocular lenses were meant to assist light transmission of the object you're focusing on and cancelling ambient light. Simply "coated" in the description means they probably only have this special assistance on the first and last lens elements – the ones you're looking at. The same can also be said of the term "multi-coated", it's probably just the exterior lens surface, but at least there's more than one layer! "Fully coated" means all the air-to-glass surfaces are coated, which is better… and "fully multi-coated" is best. Keeping stray light from bouncing around and spoiling the light you want to see is very important, but beware ruby coated lenses… These were meant for bright daylight applications and will rob astronomical binoculars of the light they seek.
Last, but not least, is a scary word – collimation. Don't be afraid of it. It only means the the optics and the mechanics are properly aligned. Most cheap binoculars suffer from poor collimation, but that doesn't mean you can't find an inexpensive pair of binoculars that are well collimated. How can you tell? Take a look through them with both eyes. If you can't focus at long distance, short distance and a distance in-between, there is something wrong. If you can't close either eye and come to focus with the other, there's something wrong. Using poorly collimated binoculars for any length of time causes eye strain you won't soon forget.
Price range for Astronomy Binoculars
So, how much? What does a good pair of binoculars for astronomy cost? First look for a quality manufacturer. Just because you've chosen a good name doesn't mean you're draining your pocket. Smaller astronomy binoculars of high quality are usually around or under $25. Mid-sized astronomy binoculars range from $50 to $75 as a rule. Large astronomy binoculars can run from a little over $100 to several hundred dollars. Of course, choosing a high-end pair of binoculars of any size will cost more, but with proper care they can be handed down through generations of users. Keep in mind little things that might be good for your applications, like rubber-coated binoculars for children who bang them around more, or fog-proof lenses if you live in a high humidity area. Cases, lens caps and neck straps are important, too.
Some Suggested Binoculars
The purpose of this guide was to help you understand how to choose the best binoculars for astronomy. But if you trust me, and just want some suggestions… here you go.
In the small end of the binocular range, Nikkon Travelite Binoculars are an excellent choice for those who want high quality in a small package.
For all purpose astronomy binoculars, I'd recommend the Celestron Up-Close and Ultima Series as well as Meade Travel View. Nikkon and Bushnell binoculars in this size range are an investment, and best undertaken after you decide if binocular astronomy and this size is right for you.
For large, dedicated astronomy binoculars you cannot beat the Celestron Sky Master or the Nikon Monarch series.
While so much information on binoculars may seem a little confusing at first, just a little study will take you on your way to discovering astronomy binoculars that are perfect for you!
Filed under: Astronomy, Astronomy For Kids
Tags: Astronomy, binoculars, magnificationRelated stories on Universe Today
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April 15th, 2008 at 1:13 pm
I own the Orion Resolux WP 10×50 Astronomical and I'm very very pleased with them.
One particular thing is they have twin focus (opossed to central focus) so you can get crystal clear focus every time (the disadvantage is that the focusing process is slow, in astronomical observations it doesn't matter because you only focus one time, but it seriously limits it's daytime capabilities). And are water proof and very rugged.
All should have a couple of nice binocs, it's very enjoyable.
April 15th, 2008 at 1:26 pm
A view of the summer Milky Way with binoculars… in dark sky… is truly breathtaking, perhaps even better than with a telescope. Even a small pair such as 6×30 shows so much.
But when I'm stuck in the city, I find I need higher magnification (like 10×50) to improve the contrast. Otherwise I just see fish-grey background sky. A pair of image-stabilized 18×50 would be perfect…. if they didn't cost >$1000!
April 15th, 2008 at 3:03 pm
The only problem, and maybe its just me, but I cant hold binoculars still. Trying to view Mars with shaky hands is annoying.
April 15th, 2008 at 5:23 pm
Kudos to Tammy for an excellent article…this is tremendous…
Re: Emission Nebula's comment…and a follow up…should we be looking for binoculars with some sort of tripod capability…to minimize shaking and stiff necks?
April 15th, 2008 at 5:24 pm
And one more question…are there any that are compatable with digital photography?
April 15th, 2008 at 7:09 pm
# Emission Nebula Says:
April 15th, 2008 at 3:03 pm
"The only problem, and maybe its just me, but I cant hold binoculars still. Trying to view Mars with shaky hands is annoying."
Indeed it is a problem with binos. There are a number of solutions though…
Try taping a broom handle or similar to the binos in some way – its inertia stops small rapid wiggles very effectively.
You can try using a tripod if you have some extra dosh to spare, and a parallelogram mount with a tripod is even more effective.
http://www.gcw.org.uk/bino/binonet.htm
But truly the best innovation for small binos has to be the Skywindow. It really makes bino viewing a pleasure, and if you can't afford one they can be made DIY with a little ingenuity and resourcefulness.
http://www.tricomachine.com/skywindow/
In relation to the use of binos for amateur astronomy – they really are the best introduction to amateur astronomy you can buy. You see a lot, learn the sky quickly and even a mediocre pair of binos will show you the sky much more effectively than a mediocre telescope.
Let me just state that again – DO NOT buy a poor quality telescope if you are starting out in astronomy, and by poor quality I mean any telescope sold at a department store, a generic 'science' shop, most camera shops and almost any telescope on ebay. Good telescopes can be had for not much outlay, but speak to a specialist telescope shop to learn about them and to sort the good-but-cheap scopes from the cheap and nasty stuff.
Really though, if you haven't been using binos for a while, then a telescope is probably too much too soon. A pair of binos and a good introductory book on the subject is the best way to get into amateur astronomy.
http://www.amazon.com/Touring-Universe-through-Binoculars-Astronomers/dp/0471513377
April 15th, 2008 at 9:45 pm
Most decent "big" binocs (9×63 and up) have tripod mount atachments.
For digital photography, I haven't seen any.
April 15th, 2008 at 9:48 pm
Tammy's going to be working on a follow up article about some easy targets to observe with binoculars. I'd love to post an article on digital cameras and binoculars.
April 15th, 2008 at 11:31 pm
I have a pair of Celestron SkyMaster 15×70, very nice, but a tripod is a must!
Not as good for viewing planets as my old 6" reflector I had as a kid was though.
April 16th, 2008 at 7:23 am
No tripod? No problem. I am going to give you a trick of the trade you're going to love! All it requires is either a broomstick, or one of those painter's extension handles that screws together in sections. What we're going to make is called a finn stick!
Holding binoculars steady isn't easy… especially if you're trying to pick out fine detail. And buying a monopod or tripod isn't in everyone's budget. Using a broomstick, seat yourself comfortably where the broomstick is at least as tall as eye level when held in front of you. Now, hold your binoculars in one hand. With the other, put the end of the broomstick under the body of the binoculars where they flex (also where the mounting holes are for a tripod.)
If you're looking at an object that is not overhead, the ground end of the broomstick should be tilted ahead of you. If it's overhead, the broomstick will be almost straight up and down. To change positions, either move the ground end of the stick towards you to support the binoculars when looking up… or away from you when looking ahead, etc.
One of the reasons the painter's poles work very well in the circumstance is because taller people can easily screw on another 1 foot section to make the finn stick longer and their seat doesn't have to be as low… But the majority of people are able to use a broom handle with ease. It doesn't take long before your hands get the trick of just where to steady the binoculars and you're off and running!
I often give binocular programs to large groups of youngsters and the Observatory simply can't afford 15 tripods… but it didn't take long to come up with 15 old broom handles! (i use the painter's poles because i'm tall, and when i unscrew the sections at the end of the observing lesson, i can easily store them all in an old tube sock. and… believe it or not… adding a crutch tip at the ground end and more sections makes it easy to make a very tall pole you can use standing up while on pavement! cost? under $2.)
Astronomy… on the fly!
April 16th, 2008 at 8:18 am
Your article on binoculars is very good. I belong to a local Astronomy club and I use binoculars constantly when we have our Outreach programs whether up on Mt. Diablo (Contra Costa County, CA) or at school programs. Many people have binoculars but they never think of them as something to use for looking up at the stars, planets, etc. After seeing the Moon and the Orion Nebula they think differently about them. A lot of families have scopes and have no idea how to use them so they are put away never to be looked at again so I tell them to take out their binoculars (if they have them) and "look up". I have several sizes including the 25×100 but they are so heavy that I don't use them that much, I also had to purchase a stronger tripod just to hold them; I use my 15×70 and 10×50 binoculars all the time. I tell people to buy a pair to enjoy the night sky.
April 16th, 2008 at 9:08 am
What about Oberwerk?
April 16th, 2008 at 12:55 pm
All the binoculars mentioned here are excellent quality. I simply cannot say enough good things about Mr. Busarow and the Oberwerk family of binoculars! Wanna' get blown away? Look through one of the giant pairs of Oberwerks!
Nikon, Cannon, Bushnell, Celestron, Meade, Orion, Leica, Ziess… these are all ones you will never be dis-satisfied with. (and i'm sure there's a lot more names i haven't mentioned!) Quite honestly, I've even picked up a pair or two that I knew were low quality and still liked them. The ones mentioned in the article were chosen because I know they're the highest quality at the lowest possible price. Just be careful of ones that you can't examine personally. It's perfectly safe to order binoculars from an internet site, but make sure you pick a reputable dealer that carries quality brands.
As for imaging with binoculars… Wow. That's a tough question. In this case, all I can do is answer from my own personal experience and invite other readers to share theirs.
I have a pair of digital imaging binoculars. When I got them, I was thrilled! At last… Now I could take some great sky shots, like Venus and the crescent Moon, you know? Guess what… Yep. It doesn't work that way. If I want to take a picture of my german shepherd digging a hole in the back 40? Perfect! But not for even the most bright astronomy applications.
But… I'm also not one to give up. (and this is going to get weird, ok?)
I've tried experimenting with photography afocally with binos. (don't eat me for breakfast, astrophotographers! i'm a writer… not a shootist!) If I remember correctly, afocally is the right word for what I did… adjust the focus with my glasses on for 20/20 vision, mated my digital camera lens to one side and took aim with the other. Did it work? Darn right it did. I've got nice images of the Moon, and bright little dots that at least I know are Saturn, Jupiter and Venus.
Now… Do the same thing with a camcorder! Only this time, you can even finer tune the focus by watching what you see on the flip side screen. Again… Really, really nice pictures of the Moon. It's not Theirry LeGault's work, but I was delighted! (pssst… an ordinary webcam works, too!)
The bottom line is, if it's not bright – it's not going to show up on film without a timed exposure and rock steady mounting. If you want to do something on that order, consider getting a spotting scope! Almost all of them come with at least a tabletop mount and quite a few have removable lenses so you can even mount the camera right on them.
Hope this helps!
April 16th, 2008 at 1:19 pm
I LOVE my Orion UltraView 10×50's Great Eye Relief and good Wide Field: best $125 spent on Astronomy Gear =-)
Mars is the wrong object to view with binox – you need well over 100x to see much of anything on Mars (on a great night).
For Binox, sweep the Milky Way in Cygnus or Cassiopia on a cool fall night – you'll soon be lost….
Another great UT article – Thanks Guys!!!
April 16th, 2008 at 2:09 pm
I bet 100 bucks that this post was written because wordtracker showed that it was a popular search term! Good SEO anyway …
April 22nd, 2008 at 11:36 pm
Are "ruby lenses" the same as "ruby coated lenses?"
May 1st, 2008 at 3:07 pm
I've found that 8×42 binoculars are great for all around use, and I would strongly recommend them for someone new to binoculars. For astronomy, stronger magnification level binoculars may be more appropriate, but you may need a tripod unless the objective lens is quite large, which can get expensive.
May 8th, 2008 at 6:06 am
Hello!
I periodically check back for questions, so please pardon the delay.
Yes, ruby lenses and ruby coated mean essentially the same thing… But these are NOT good coatings for astronomical binoculars. Ruby coatings were meant for daytime applications to reduce glare and will significantly destroy the light from astronomy targets.
May 18th, 2008 at 6:52 pm
can i see saturns ring thru a 7×50? or 10×50?
im a newbie in astronomy.
June 3rd, 2008 at 12:23 am
hey just one questionn how does light behave when it travels through binoculars to your eye??
June 12th, 2008 at 2:15 pm
How would you combine lenses if you wanted to magnify 100X?
June 13th, 2008 at 1:46 pm
I'm looking to get started in the best way so I've decided to purchase a "double telescope". I am comparing these 9X63 found at Amazon.com. They are:
PORRO
Celestron 72023 Skymaster ($300)
Orion Mini Giant ($200)
ROOF
Meade Astro ($120)
Barska Blackhawk ($90)
Tasco Low Light ($150)
Can someone explain why I shouldn't buy the Barska Blackhawk? Are the Celestron and Orion worth that much more, and why? I'm an amateur. Be nice. And thanks.
June 30th, 2008 at 11:04 pm
hello every one!
we all know that binoculars are great for observing even if you have a telescope you sometimes take a pair of them to observe the night sky.now i have my 20*90 binoculars…they are very nice and i love them so much…
good luck…
October 16th, 2008 at 5:02 pm
hi, ty!
i just happened to notice you'd replied to this topic. there's nothing wrong with the barska blackhawks except for they are coated for daytime observing and not for night. if you're a bird watcher, these are fine. but if you're primarily interested in using them for astronomy, the coatings will dim the starlight considerably because they were meant to reduce daytime glare.
hope this helps!
October 16th, 2008 at 5:04 pm
oh! ps…. you don't want to use roof prism binoculars for asto applications, either. they also dim the image.
November 8th, 2008 at 1:04 pm
Hi Ty…Just looking at your question and if you look back at the higher priced "astro" binoculars you will notice that they have much larger lenses, hence the higher prices. The Barska's have a 43 mm lens compared to Celestron's 72023 63 mm lens. Bigger lens, brighter image, more to see!
Cheers
November 8th, 2008 at 1:14 pm
Whoops …my bad… Barska does indeed sell a 9×63 roof prism for astronomy. Seems they use "blackhawk" for a whole series, not just one model. Must learn to read.
Still…compare the specs carefully, and read the reviews to see if Celestron and Orion can justify the higher prices.
December 24th, 2008 at 5:36 pm
Celestron binoculars are the best!
April 2nd, 2009 at 6:21 pm
Haha ^^ nice, is there a section to follow the RSS feed