Barlow Lens vs Eyepiece – Magnification Battle

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If you are looking for higher magnification with your telescope, you have two options: buy the Barlow lens or get a shorter eyepiece to your collection. But what is a better option to increase the magnification? Barlow lens or the eyepiece? They both have their advantage and disadvantage.

Barlow lenses are a better option if you want higher magnification. They maintain the eyepiece’s eye relief, and you can use them with any telescope or eyepiece you already have. If you use an eyepiece with a shorter focal length to increase the magnification, you get shorter eye relief and only one magnification.

Opting for a high-quality Barlow lens is also a cost-effective method to get more magnification options from your current eyepieces. It will effectively double or triple the eyepiece collection you have.

Let’s take a closer look at why the Barlow lens is better by explaining the basic differences between the Barlow lens and the eyepiece. But first, we need to understand how the magnification is calculated when using the telescope with a Barlow lens and the eyepieces.

How to Calculate the Magnification of the Telescope

It is straightforward to calculate the magnification of any telescope if you know all the parameters. These parameters are the focal length of the telescope and the focal length of the eyepiece.

Divide the focal length of the telescope by the focal length of the eyepiece. Let’s say you have a telescope with a focal length of 1000mm, and it comes with two eyepieces: 20mm eyepiece and 10mm eyepiece.

You will get only two magnifications in this example, 50x magnification with 20mm eyepiece and 100x magnification with 10mm eyepiece.

So if you need more options, either less or more magnification with the telescope, you have to consider expanding the eyepiece collection or buying a Barlow lens. 

What is Eyepiece in Telescope

I hope you already know what eyepiece is but just in case, let me clarify it. The eyepiece or ocular is an optical instrument that is attached to the focuser of the telescope. Without the eyepiece, you can’t use a telescope(well, you can if you use a camera, but that’s a different topic).

Barlow lens is not an eyepiece, and you still need an eyepiece if you are using the Barlow lens in the focuser.

Telescope eyepieces come in different focal lenses and sizes. There are also many types of eyepieces you can choose from. The most common eyepiece design is the plossl eyepiece. Plossl eyepieces usually come with the telescope in the box.

Eyepieces with different focal lengths will give you different magnifications. By changing the eyepiece in the focuser, you are changing the magnification of the telescope as well.

The shorter focal length will provide more magnification, and a longer focal length is providing less magnification. 

You can also get a zoom eyepiece. This eyepiece will provide a zoom feature like a camera lens. But as with all special accessories for a telescope, it is quite an expensive toy.

Astromania 1.25″ 8-24mm Zoom Eyepiece

To learn more about eyepieces, read my telescope eyepiece guide for beginners.

What is Eye Relief of the Eyepiece

Eye relief is the distance in millimeters between your eye and the eyepiece glass, where you can see the eyepiece’s full field of view. Why is this important?

Optics showing eye relief and exit pupil
1 Real image   2 Field diaphragm   3 Eye relief
4 Exit pupil
Tamasflex / CC BY-SA

If you have an eyepiece with very short eye relief under 10mm, it can not be pleasant to observe with it. Short focal length eyepieces tend to have very short eye relief. 

So if you want higher magnification, you need to use a very short eyepiece with short eye relief. This is also a big problem if you wear glasses. 

It is not an issue for some people, and there are high quality but expensive short eyepieces with decent eye relief. 

What is Barlow Lens and How it Works

Barlow lens is a must-have optical instrument that should be in every amateur astronomer inventory. Barlow lens is purely made to increase the magnification of the telescope.

Barlow lenses have different magnification multipliers. The most common are 2x, 3x, and 5x. These numbers are telling you how much Barlow will increase the focal length of the telescope.

Remember the magnification formula in our example with a 1000mm focal length telescope? This is where the magnification coms from. It is not affecting the focal length of the eyepiece, only the focal length of the telescope.

Now do the calculations again with those two eyepieces, 20mm, and 10mm. Let’s say we have 2x Barlow.

When you use this Barlow with that telescope and eyepieces, you will get two additional magnifications.

20mm eyepiece + 2x barlow = 100x magnification

10mm eyepiece + 2x barlow = 200x magnification

The telescope’s focal length doubled(from 1000mm to 2000mm), hence the double magnification with the same eyepieces. Now you have 4 eyepieces and 4 magnifications using one Barlow lens.

Another advantage here is that you can use an eyepiece with longer focal length and comfortable eye relief to get the same magnification than with shorter ones with short eye relief without the Barlow lens.

That’s’ why it is better to buy one Barlow lens than buying more eyepieces. It is a much cheaper solution if you want more magnifications.

“Less Glass is better” Myth

Less glass is better was true some years ago or when using very old accessories for the telescope. It means that if you incorporate more glass elements in the light train of your telescope setup, you will be losing light and quality of the image.

Using a Barlow lens in the focuser with the eyepiece is more glass in the light train. But modern optics came a long way, and nowadays, more glass results sometimes in a better image. 

You will be losing some light; of course, you can’t cheat physics, but it is negligible, and you won’t notice it with the naked eye.

Buying a Barlow lens with more optical elements inside is also crucial. Low-quality Barlow lenses using only one optical element will destroy the quality of the image. The higher end of the Barlow lens is Powermate with 4 or more optical elements.

You should check my article Powermate vs. Barlow lens, and if you are considering buying a Barlow lens, then go to my buying guide, The Best Barlow Lens.

Barlow Lens vs. Eeyepiece Conclusion

What is my final conclusion on Barlow Lens vs. Eyepiece for you? It depends. It is up to your personal preference and setup you are using. Some amateur astronomers would argue with me for sure that using only the eyepiece is better than using a Barlow lens. 

But from my personal experience, I believe that the Barlow lens is the best option for a beginner to squeeze more magnification from the telescope. I have collected many Barlow lenses over the years, and I’m still using them. 

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