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10mm vs 20mm Eyepiece [What’s The Difference?]

Telescopes are complex pieces of equipment that allow us to see far into the night sky in immense detail. However, they require numerous components working together to achieve such an outcome. One of the most important of all is the eyepiece, as it has a direct correlation to magnification and your overall viewing experience. But when it comes to choosing between eyepieces, it’s easy to get confused by the numbers. So if you’re not sure whether to opt for a 10mm or 20mm, you’ve come to the right place.

So, what are the differences between a 10mm vs. 20mm eyepiece? The main difference between a 10mm and a 20mm eyepiece is the diameter, which has implications on magnification and field of view. A 10mm eyepiece will provide more magnification, yet will have less field of view than a 20mm. Thus, they are used to observe different celestial bodies; a 10mm often the Moon and planets, a 20mm Deep Sky objects like star clusters.

You’d be surprised to learn there are quite a few differences, even if they’re meant to provide similar features. We’ll be looking into these shortly.

Just consider, that astronomers choose one over the other for different reasons, though most consider magnification to make their choice. 

No matter which telescope you choose, the eyepiece is a big part of the quality it’s able to provide.

In this guide, you’ll learn about the ins and outs of a telescope’s eyepiece and the key differences between a 10mm and 20mm.

What Is The Difference Between a 10mm vs. 20mm Eyepiece?

There difference between a 10mm and 20mm are the dimensions of the lens and the capabilities of their magnification. 

For starters, 10mm eyepieces have a smaller diameter than 20mm. 

This also correlates to the focal length. With a higher focal length, an eyepiece will be capable of greater magnification.

Some may argue that there isn’t a huge difference between a 10mm and 20mm eyepiece, but the core of their construction says otherwise. 

It’s also important to note that eyepieces with a bigger diameter come with a wider field of view, which allows more clarity and detail for your viewing experience.

When it comes to magnification, it’s known that a 20mm eyepiece is 50% stronger than a 10mm, which only has the ability to offer medium-low magnification. 

Although this may be more than enough for some people, those who are looking for better magnification in addition to image detail would prefer a 20mm eyepiece.

To specify a little further, a 10mm eyepiece carries a 41° FOV, while a 20mm boasts a 56° FOV. 

It might not seem like they’re too far off from each other, but the difference can definitely be seen when in use. 

Once again, it’s not that a 10mm offers poor visual quality; you just won’t get as much detail as you would with a 20mm.

What Is A 10mm Eyepiece Good For?

If you’re only looking to observe close-up celestial objects, a 10mm eyepiece is more than sufficient. It’s not meant for deep-space objects, and you won’t get a pristine level of detail in your image, but it still has the capability to provide plenty of wonder. 

Most people are happy with a close-up shot of the moon and a more magnified look at star clusters. 

Considering the moon doesn’t look the exact same every single day, you have plenty to observe with a 10mm eyepiece.

Of course, if you’re looking for better magnification and detail, you may want to look into a 20mm, but that doesn’t mean it’s necessary.

If you talk to others who use a 10mm eyepiece, you’ll notice there are plenty of astronomers who are more than satisfied with it.

I feel it’s also important to mention that a 10mm eyepiece may not be the best for tracking objects due to its FOV and overall viewing quality. 

However, many objects that are more stationary shouldn’t be hard to find. 

It’s a great starting point for those who are new to telescopes, as it allows you to test the waters of what your preferences might be.

It’s also known that 10mm can be a little less comfortable than those with a longer eye relief. 

There’s a lot you can modify to make your experience as comfortable as possible, but 10mm may not be the best option for extended viewing sessions.

At the end of the day, which telescope you choose and the components you want will come down to personal preferences.

It’s always a good idea to take advice from those who have been in your position, but if a 10mm is suitable for your needs, then it should be more than enough. 

Of course, you can always upgrade if you feel that you’ve outgrown what it has to offer, and many telescopes have the ability to be customized so you can switch out specific parts.

What Is A 20mm Eyepiece Good For?

Featuring a few upgrades in comparison to what a 10mm can offer, 20mm eyepieces are great for low-power scanning of star clusters in addition to bigger galaxies and even nebulas. It delivers a broader scope of what you’re able to see, and its viewing capabilities will provide a satisfying experience for a long time. 

You should expect a 20mm eyepiece to be more expensive, which means the total cost of the telescope will be as well.

If you’re hoping to see outer space in more detail with better magnification, a 20mm eyepiece is a pretty decent choice. 

It provides a viewing quality that’s satisfactory for novice and more experienced stargazers, and you’ll never run out of celestial objects to look for.

Whereas a 10mm eyepiece focuses on close-up observations, a 20mm is built for essentially the opposite outcome.

For those who are looking for a broader look at the night sky, a 20mm eyepiece would be your best bet. 

Although having the ability to achieve a close-up view can be great, it may limit you in some ways. 

With a 20mm, you can see much more at once, which is a preference for many astronomy enthusiasts.

It’s important to know these differences as the slightest change in components in a telescope can be a deal breaker for some people. Nevertheless, both eyepieces have something unique to offer, but they cater to a specific viewing experience. Another aspect to consider is that a 20mm eyepiece is bound to be more expensive than a 10mm, which is an important factor for many people when shopping for a telescope.

Is a 20mm Eyepiece Better Than 10mm?

It isn’t that a 20mm eyepiece is better; the main difference is that they’re both built for different outcomes. A 10mm is great for close-up images, while a 20mm offer a broader view of the night sky, including more objects in your view. Then again, there are many people who would agree a 20mm is better, but this would be based on their personal preferences.

Both eyepieces have something unique to offer, and although they can be compared in many ways, each eyepiece is built for a specific viewing experience.

When choosing a telescope or a specific eyepiece, you want to consider the differences mentioned in this article, as they will directly affect the outcome of what you’re able to see.

If you want a close-up look, a 10mm would be best for you, but if you’d rather view more objects at once, you might want to look into a 20mm eyepiece. 

The two eyepieces mentioned in this article are pretty standard for many telescopes, but there’s a lot more variety when it comes to this component of a telescope.

No matter which one you choose, they both have the ability to provide a memorable experience, but knowing their ins and outs will make it easier to decide what’s optimal for you before you make a purchase. 

In short, a 20mm eyepiece is only better if you’re looking for a particular view, but a 10mm is more than capable of satisfying many people who prefer close-up shots.

Things To Consider When Choosing The 10mm or 20mm Eyepiece

One of the first aspects you want to consider is the viewing experience you’re looking for. The eyepiece will have a significant bearing on what you’re able to see, regardless of the other components on your telescope. Outside of that, there are numerous considerations you should take into account.

The construction of the eyepiece itself, the comfort it provides, and if it’s sufficient for extended viewing sessions are rarely considered. 

On another note, it can be challenging for people who wear glasses to effectively use an eyepiece. 

However, there are a variety of eyepieces that are much more comfortable than others in that regard. 

It’s a good idea to look into eyepieces that reduce chromatic and spherical aberration, which can become worse when wearing glasses. 

You also want to consider the focal length and magnification you want, as each eyepiece will be different here. 

Some variations are more drastic than others, but all of these minor points play into your overall experience when using a telescope.


Finally, once you’ve gone through all of the features and specifications of the eyepieces you might want, you’ll want to factor in the potential costs.

For some individuals, this can make or break their purchase decision. 

A 20mm eyepiece will generally be more expensive in this comparison, but the viewing experience an eyepiece provides should be the top concern on your list.

Relayed eyepiece guides you may want to check out: