Essentials for Buying the Best Binoculars for Astronomy

There are many designs of binoculars which have been cultivated over the centuries. Finding the right pair for you can be tough with the many types and features of modern-day equipment. I hope this article will help you with your decision.

Telescope or Binoculars?

Making the choice of binoculars or a telescope can be very difficult. However, here is a list of pros and cons for each:

Binoculars:

Pros:

• Comfortable Viewing
• Cheap
• Three-dimensional viewing
• Wide field of view
• Images = Right Side up
• Let in more Light

Cons:

• Cannot magnify Far Beyond 15
• Unless you get larger aperture binoculars, it can get hard to see stars or other celestial objects
• Large magnification binoculars (12 times and above) often require tripods
• Most people over 30 can’t see the difference in light

Telescopes:

Pros:

• Offers greater magnification than any pair of binoculars
• Offer lenses that allow views of various celestial objects (like the sun)
• Large telescopes let in more light than binoculars

Cons:

• High Maintenance
• Requires tripods
• Upside down images

Examining the Details & Finding the Right Binoculars

When buying binoculars, there are many features to look at. These features often have a number associated with them, and others are more of a style difference. Most of these features are stamped on the binoculars as numbers on the side, or details on the packaging. Others you may have to calculate the number. Here are some common characteristics to look at:

Magnification and Aperture

When looking for binoculars, there are always two numbers given with each pair. These numbers are the magnification and the aperture. They generally look something like this: “8 × 42”.

The first number is the magnification. For the above example, the magnification is eight times what you would see with the naked eye. Which magnification you use is completely up to you. Generally, most beginners start off with a 7x or 10x magnification.

The second number is the aperture. It is measured in millimeters. It determines how much light is let in. The smaller the aperture, the smaller the field of vision, and the less light you will have. For astronomy, almost everyone uses at least an aperture of 50 mm. Often times, you should look at the magnification and the aperture together.

When you want to know how bright something is going to look, you need to divide the aperture by the magnification. Let’s say that you have a “7×50” pair. The exit pupil will be a little more than 7 mm wide (50 mm/7 ≈ 7.14). The pupil of your eye can only open to 7 mm under ideal conditions (very dark).

Warning: After age 15, your pupils will slowly stop opening up as wide. At age 15 they can open to 9 mm. At age 25 they open up to 7 mm. The pupils for most people over the age of 30 will only open to 6 mm. After age 50 almost everyone’s pupils will only open 4 mm or 5 mm. Consider these factors when buying binoculars, as the extra light let in from a pair with an exit pupil of 7 mm might not be worth the lower magnification.

As you get more adept, you may wish to buy a new pair of binoculars with higher magnification. As you increase magnification, you should also increase the aperture. More advanced astronomers recommend a 70+ mm aperture. You may eventually wish to buy a telescope, as they offer excellent magnification and aperture values.

Field of View

The field of view is also a set of numbers stamped on binoculars. It is often put in # of feet at 1000 yards. Here is an example: 367 ft at 1000 yds. This would be the equivalent of a 7° field of view (or around 14 times the size of the moon). If you live in a country with the metric system, it will be put in # of meters at 1000 meters.

The better measurement for binoculars is the angular field of view (FOV). This is the angle in degrees you should be able to see through your binoculars. Normally humans can see right around 180, but we focus on about 3°. You can technically calculate out the angular field of view using the number of feet (or meters), but the resulting equation is really complex, so I recommend going to the website for the info (or if you’re at a physical store, asking the person over the counter for help).

Some binoculars offer special wide-angle views. Be warned, these pairs often have bad distortion of the stars at the edge of the field of vision. However, all lenses have some distortion, so you need to weigh the benefits and the costs for which model you would prefer to use.

Eye Relief

Eye relief is the distance your eye should be from the exit pupil in order to get the proper focus and field of view. As a rule, the larger the eye relief, the more comfortable for viewing, however too many of the cheaper models have small eye relief values.

If you wear glasses on a regular basis, you should continue to wear them when looking at objects through binoculars. In order to make sure that you have a comfortable time viewing through them, though, you should look for a pair that has an eye relief of at least 15 mm (the absolute minimum). Roll-back eye cups are also essential, so that they aren’t rubbing against your glasses. The optimal eye relief value for people wearing glasses is around 17 mm.

For those not wearing glasses, it is generally recommended that you have an eye relief value of at least 9 mm. Anything closer will be quite uncomfortable for viewing. Eye cups help block out other sources of light and prevent you from poking your eyes with the exit pupils, so look for binoculars that offer this feature. For better viewing is at least 11 mm.

Prisms

There are two main types of prisms when it comes to binoculars, Porro prisms and roof prisms. When it comes to viewing for astronomy, Porro prisms are the only one you want. Roof prism tend to distort the incoming light of stars, comets, and meteors, and are also more expensive. Only the most expensive models with roof prisms have no light distortion. Porro prisms, on the other hand, are cheaper, and offer very little distortion. The only drawback is that they are slightly bulkier. I recommend Porro prisms over roof prisms for almost every amateur application.

Lens Coatings

There are many coatings, all of which serve different functions. When considering binoculars of similar specifications, it is often the coating which can make the major differences. Here some different coatings you should consider when buying binoculars.

Optical coatings give the lens a tint when looking at it (of blue, green, red or golden amber). These coatings, however, don’t change the color of the objects, but rather increase the amount of light coming in through the binoculars. You can often tell a low-cost model from a medium/high-cost model by the number of coatings the lenses/prisms have on them. Low-cost models generally only have one coating on the lens. High-cost models generally have multi-layer coatings on all the surfaces (lenses, prisms, etc.).

You should also look for binoculars that are waterproof and/or have rubber armor to protect the lenses. This will protect them from scratches, mold, fungus, algae, dew, and other problems. Also, look for fog resistant coatings (normally instead of fog resistant coatings, though, the barrels are nitrogen purged or vacuum sealed), and heat-resistant coatings, as these will help improve what you see on nights that are particularly cold, or particularly warm.

 

Top Picks for Your Price

Which model you should get, depends on how much you want to spend, and which features you want. Here is a list of good choices listed by price (from lowest to highest). You will probably want to start off with a 7×50 or a 10×50 pair of binoculars. At the bottom I will also include a good high-power pair of binoculars.

Note: High-power binoculars are pricier. The good quality high-power ones often can come with over $1000 price tags. Like all binoculars, be sure to test them out in person before you try them out. If you attend an astronomy club, ask someone who owns a pair if you can test them out (by looking through them).

Low Price Binoculars (0-$49.99)

Celestron 71198 Cometron (7×50):

This model costs $34.95. It offers multi-coated lenses, is water resistant (but not waterproof), and weighs around 27 ounces. This model comes with an aluminum housing and rubber shielding. 6.8° angular field of view. It has an eye relief of 13 mm. It has an exit pupil of 7.1 mm.

Medium Price Binoculars ($50-$149.99)

Orion 10151 (10×50) E-series:

This model costs $79.99. The features that immediately stand out are the 19 mm eye relief (very good), and this model is completely waterproof. It has fully multi-coated lenses, rubber shielding, and many other features. This model is waterproof, and has an angular field of view of 6.5°. Has a 5.0 mm exit pupil. It weighs 2.2 lbs.

Celestron 71348 Outland X (10×50):

This model costs $105.99. This model has an eye relief of 10 mm and multi-coated lenses. It is the lightest model for this section weighing in at 27.1 oz. It is completely waterproof. Has a 5.5° angular field of view. Nitrogen filled (making it fog resistant). It has a 3.1 mm exit pupil.

Gosky Titan (20×80):

This model costs $149.99. It has many features: multi-coated lenses, rubber armor, aluminum framework, and protective shielding. Unlike other binoculars, this one can be easily attached to a tripod, and has an easy cellphone stand (for taking photos with your cellphone through your binoculars).

High Price Binoculars ($150+)

Orion 09466 (15×63):

This model costs $233.48. It has an eye relief value of 19 mm. In addition, it has a hard case, a wide neck strap, and a lens caps. It is fully multi-coated (every lens and prism is coated in multiple layers). The barrels are threaded so that glare is eliminated, and has an exit pupil of 4.2 mm.

These are just example binoculars. If you don’t like any of these options, there are dozens of others. I hope this article helps you in making your decision regarding your choice of binoculars. Have fun!

If you found this article helpful, be sure to check out other articles at planandorganize.com. There are many helpful articles about a large variety of subjects.

Sources:

Roy, Rob. “Aging Eyes and Pupil Size.” Amateur Astronomy 23 Oct., 2013. Amateur Astronomy. 3 Sept., 2019. <https://web.archive.org/web/20131023134125/http://amateurastronomy.org/Events/EH361.html>

Ting, Ed. “Binoculars for Astronomy: Ultimate Guide to Selecting and Buying.” Sky and Telescope 30 July, 2015. American Astronomical Society. 3 Sept, 2019. <https://www.skyandtelescope.com/astronomy-equipment/binoculars-for-astronomy/>

Johnson, Paul. “How to Buy Binoculars.” Optics Reviewer. 3 Sept., 2019. <https://www.opticsreviewer.com/how-to-buy-binoculars.html>

“Binoculars.” 30 Aug., 2019. ­Wikipedia. 3 Sept., 2019. <https://en.wikipedia.org/wiki/Binoculars>

Burnham, Robert, et al. ­A Guide to Backyard Astronomy: Your Guide to Starhopping and Exploring the Universe. San Francisco: Fog City Press, 2002. Print.