Astronomy binocular buying guide

The Essential Astronomy Binoculars Buying Guide

There’s a lot of binoculars out there for different purposes. And obviously, no one type is suits it all. So its important to know which type of binoculars will be best for your needs. 

Here’s the special guide for those of you looking for astronomy binoculars. In this super easy guide, step-by-step, you’ll learn; how to choose your next astronomy binoculars. 

But wait! Before we go any further, lets headstart with the definition first!

Astronomy binoculars

Binoculars at the very base are nothing but the pair of parallel telescopes joined at the center by a hinge for suitable adjustment. Due to the larger lens, they collect more light and thus we can see distant things.

These astronomy binoculars are no different except for optical quality which is quality consciousness.

Specifications you need to focus on

Internal structure of Porro prism binoculars

The internal design of Porro prism binoculars. Image Source: Wikipedia

To be an efficient buyer, it’s important to know some basics of binoculars. If you only understand properly, this guide will surely make you a standalone binoculars expert at no doubt.

So we got to dig deeper.

Following are the specification you need to focus while choosing astronomy binoculars:

  1. Aperture
  2. Magnification
  3. Eye relief & Exit pupil
  4. Field of view
  5. Weight

Lets headstart with the big one.

1. Aperture ( Objective lens )

porro prism vs roof prism binocular

Note the difference between the two designs.

Call it the eyes! The objective lens is the front lens on the binocular which gathers light from the object you are viewing. It consists of two glass elements glued together.

In optics jargon, this is called a compound lens which reduces distortion. The light then passes through the Porro prism (or roof prism in a more compact design).

Coming to the point. Your astronomy binoculars should boast at least 50mm of this aperture.

A larger objective lens diameter means more light enters your eyes. However, a larger objective lens also means a larger and longer binocular body.

If you want to a convenient pair of astronomy binoculars, the objective lens of 50mm is best.

But it doesn’t mean you can buy that 500 rupees 50mm binocular and expect to stargaze. It WON’T work! At least with astronomy, you need to go with quality.

My advice will be to go with trusted manufacturers like Celestron or Olympus.

2. Magnification

You may not follow this thing which I am about to say – but you got to believe this. It doesn’t matter a lot. The magnification doesn’t just play a big role.

For astronomy application, magnification generally ranges from 8x  to max 20x. Anything higher than the power of 20x is undesirable and requires a tripod for several reasons:

(i) the amount of light reaches the eyes decreases with increasing power so that the object appears darker at higher magnification;

(ii) the field of view decreases with increasing power; and, most importantly,

(iii) the higher the power, the more sensitive viewing is to any little movement.

As a matter of fact, viewing through a pair of 15x binoculars is an exhausting experience because even your heartbeat or breathing make the image dance around!

Another advice: Avoid buying a zoom binocular! You may think it is useful to change the power of magnification, but it’s cumbersome, difficult to use, and easily broken.

3. Exit pupil & Eye relief

There is also a practical limit on the size of the objective lens. This is determined by the exit pupil of a binocular.

For an 8×50 binocular, divide 50 mm (objective lens size) by 8 (power of magnification) gives 6.2 mm, which is the size of the exit pupil of that binoculars.

If you want to take full advantage of a large objective lens, i.e., to collect all the light funneled through the binocular, the binocular’s exit pupil cannot be larger than your eye’s entrance pupil (you know, the black hole at the center of your eyeball). This is where the limit comes in.

The entrance pupil of a human eye changes with the light condition, but the maximum size is limited by age.

The entrance pupil can reach 8 mm for a teenager but is only ~4 mm for a 50-year-old.

For an entrance pupil of 5 mm, a 7×35 is just as good as a 7×50, but the latter is much heavier.

Finally, those my eyeglass friends should go for a long eye relief binocular to get more comfortable.

4. Field of View

The concept of FoV is simple. Its the portion of the scene you can see with complete details via binoculars. It’s usually given as degrees or as length at 1000 yards (shown below).

The FoV usually ranges from about 2 to 10 deg and depends on the design. Our universe is huge, so obviously its better to for largest possible FoV device.

5. Weight of binoculars

Now, this thing will vary from person to person and how you want to use your devices. If you are a muscle or planning to use a tripod then you are good to go with that bulky binoculars. 

On the flip side, a compact binocular weighing less than a KG is good for carrying around and to travel with.

FAQs on Binoculars

I hope you got the complete picture of the binoculars mechanism from above. Now let’s answer some of the most popular FAQs you guys have been asking.

1. What do the numbers on binoculars mean?

Binoculars are specified mainly by two numbers, e.g., 8 x40, the first for the factor of magnification and the second the objective lens diameter in millimeters(mm).

2. Can you see planets with binoculars?

Definitely! It’s, in fact, is recommended to beginner astronomers to start with binoculars. But wait. Not every binoculars. You need at least 10×50 binoculars to see planets. This should also be of high quality. We call them astronomy binoculars

3. Which binoculars are best for astronomy?

Top quality binoculars like Celestron, Olympus, and Nikon with at least 10x magnification and 50mm aperture are best for astronomy. Find some here

4. Can you see rings of Saturn with binoculars?

Yeah, you can! Get a 12×60 or higher, a tripod and some practice will make a big difference.

Conclusion

Astronomy binoculars are special. The most important criteria you need in choosing them is aperture size, its quality, magnification, and weight.

The first spec we need to decide is the aperture. For astronomy purposes, can’t tolerate anything less than 50mm.

And for higher magnification, more than 15x, you will want a tripod.

So that’s it! I have some handpicked recommendation for you in my binocular section. My favorite is SkM12x60. Go check them! And if you have a question or two, go ahead and ask me below!