How To Use A Barlow Lens: Our Guide For Telescopes And Astrophotography

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How To Use A Barlow Lens

If you want to know how to use a Barlow lens on a telescope, or to take your astrophotography to the next level, you're in the right place!

Barlow lenses can increase the magnification of your telescope, meaning that don't necessarily need to go for a larger telescope if you want to increase working distance. And the good news is that they are relatively inexpensive and give you stunning output.

Unquestionably, they are a great addition to your telescope, but they can be quite difficult to set up and use. In this guide, we will be going over how to use one for astrophotography as well as on a telescope. Let's jump in!


What Is A Barlow Lens?

How To Use A Barlow Lens
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Barlow Lens

Barlow lenses are optical elements that increase the magnification of your telescope. In simple terms, introducing a Barlow lens into the light path of any type of telescope increases the effective focal length, resulting in an increase in magnification.

They are named after Peter Barlow, an English physicist and mathematician, who developed these lenses in 1833. He has nothing to do with Coronation street, as far as we know.


As an illustration, if your 900mm focal length telescope produces 90 times magnification with a 10mm eyepiece, a 2X Barlow setup can produce 180 times magnification.

Barlow lenses are available in a variety of designs and you can find them in a wide range of price points. The most common one is a 2X Barlow which doubles the magnification of any eyepiece. Barlows are also available in 2.5X, 3X and even 5X magnification. For most people, 2X will be more than adequate. You can get a good quality 2X Barlow lens for under $50 from Amazon.

As mentioned above, the Barlow lens is a cost-effective way to increase the magnification of your telescope. Also, they effectively double your eyepiece collection.

Let's say you have the following three eyepieces: 25, 16 and 10mm. If you were to get the same doubling of magnification, you would have to purchase 12, 8 and 5mm eyepieces. But with one 2X Barlow lens, you can effectively get that same magnification with your eyepieces.

In other words, it is a lot less expensive than buying another shorter focal length eyepiece. Barlow lenses will make your astrophotography and stargazing better without burning a hole in your pocket. We recommend high-quality Barlow with a minimal reflection for better quality images.


How To Use A Barlow Lens

A Barlow lens is very easy to set up with a little guidance. Barlow lenses are typically used for stargazing and astrophotography. Here, we’ll describe how to use a Barlow lens for stargazing as well as astrophotography. Keep reading!

How To Use A Barlow Lens On A Telescope

The Barlow lens is typically inserted between the diagonal and the eyepiece, for refractors and Schmidt-Cassegrain telescopes. For reflectors, the lens is inserted directly into the eyepiece holder of the focuser drawtube. Here is how to use the lens on a telescope:

  • First of all, remove your eyepiece from the telescope.
  • Then, insert the Barlow lens with the “nose” (the smaller side) in the direction of the slot where you would normally insert the eyepiece. This can be into the telescope’s focuser or the star diagonal.
  • Now, insert the eyepiece into the open slot at the end of the Barlow, also with the “nose” pointing to the opening.
  • Finally, secure both the Barlow and the eyepiece with the locking mechanism they have (dial, screw, etc.).

It's essential to make sure that the Barlow lens has a barrel size that matches the eyepiece you intend to use it with. This is the diameter of the eyepiece tube that fits in the focuser. Typical sizes are 0.965 inches, 1-1/4 inches, or 2 inches.

How To Use A Barlow Lens For Astrophotography

How To Use A Barlow Lens
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As noted above, Barlow lenses are used for astrophotography. If you are new to astrophotography, you may be wondering how to use Barlow lenses. 

For astrophotography, you need to get a T2 adapter for your camera. If you are using a planetary camera such as a ZWO ASI 120 MC, the adapter is included. But, if you using a DSLR or mirrorless camera, you need to buy one. With that in mind, let's see how to set up the lens for astrophotography:

  • The first step is to mount the T2 adaptor with the nosepiece on your camera and insert it in the Barlow.
  • Next, insert the nosepiece of the Barlow in the back of the scope or in the focuser, and you are all set.
  • Finally, secure both the Barlow and the camera (adapter) with the locking mechanism they have (dial, screw, etc.), and you are all set.

Now that you know how to use the Barlow lens, let's gaze at some exquisite stars and planets. We recommend looking at the second-largest planet in our solar system with unmistakable rings!

Barlow Lens Pros and Cons

As we suggested above, a Barlow lens can effectively double the number of lenses you have at your disposal, without going to the expense of buying all those additional eyepieces. This is a major advantage.

They also work alongside your eyepieces without affecting the field of view. This can be particularly beneficial for anyone who wears glasses, as they will be able to enjoy a full field of view, even at high power, without having to remove their specs.

However, there are some potential drawbacks to be mindful of. A poor quality Barlow lens can negatively impact the colours that you see, as well as potentially distort the image in other ways.

Additionally, more powerful Barlow lenses don’t work especially well with smaller telescopes. A smaller telescope can struggle to pull in a lot of light, so using a powerful Barlow with these will deliver dim images.