Best Barlow Lenses For Your Telescope

Invented by optician Peter Barlow, the Barlow lens is often capitalized due to its eponymous nature. A common optical component, this device slots between the telescope’s eyepiece and either its objective lens or primary mirror. In a standard setup, the eyepiece comfortably fits atop the Barlow lens, which then inserts into the diagonal, or focuser—the regular resting place for the eyepiece.

The chief aim of integrating a Barlow lens within the telescope’s optical pathway is to increase the magnification offered by any eyepiece or to increase the telescope’s focal length for photographing the planets. By owning just a single telescope Barlow lens, you effectively expand the potential magnification options available in your collection of eyepieces. This not only offers cost savings but also simplifies your magnification choices.

Also Read: How to Use a Barlow Lens and How Does It Work?

In a broad overview, the dual-element Barlow lens has emerged as the popular choice in the industry. It’s advisable to steer clear of Barlows with just a single lens element, often bundled with cheaper telescope models. While they might serve their purpose, they’re known to create optical aberrations and ruin the view.

For optimum results, a Barlow lens should integrate seamlessly without introducing any optical distortions or diminishing the field of view. The view output from a 10 mm eyepiece combined with a 2x Barlow should be almost identical to that from a 5 mm eyepiece of the same design. If this isn’t the case, it’s an indicator of the Barlow lens’ inferior quality or design flaws.

Best Barlow Lens For 1.25” Focuser: My Recommendations

It’s likely that you are going to want a 1.25” Barlow over a 2” one. For planetary imaging, it’s all you need, and most shorter focal length oculars that you’d want to use with a Barlow are 1.25” anyway. A 1.25” Barlow is also cheaper and much lighter in weight than a 2” unit.

1. Under $20: NEEWER 2X Barlow Lens

This Barlow is a basic, no-frills generic option offered by many brands. It provides standard 2x magnification and, in most telescopes, adds minimal additional glare or chromatic aberration. It also has T-threads at the top to directly attach a DSLR or mirrorless camera, though these are far from the best cameras for the planetary imaging for which a Barlow is suited. However, those with a keen eye will likely want to spend more on a higher-quality unit.

2. Between $20 to $40: GSO 1.5X/2X Shorty Barlow Lens

GSO 1.25" 2x "Shorty" Achromatic Barlow Lens
GSO’s 2x Barlow is a two-lens element design that features full multi-coating. It is a little higher-quality than the generic units sold at lower prices. Just like GSO’s 2” Barlow, this one has a removable 1.5X element, which effectively gives you two additional magnifications for each of your eyepieces. GSO does offer a version of this Barlow with T-threads for a slightly higher price, should you need it.

3. Between $40 and $100: GSO 2.5x Barlow Lens

BL251 GSO 2.5x Barlow Lens
GSO’s 2.5x Barlow is ideal for those who want a Barlow for both planetary imaging and visual purposes, offering a bit more of a focal length boost than a 2x but not amplifying too much. The brass compression ring offers a secure fit to your eyepiece, and this Barlow uses an ED lens element to reduce chromatic and other aberrations.

4. Best $100-$200 Choice: Tele-Vue 1.25” Barlow

Tele-Vue 1.25” Barlow
The Tele-Vue Barlow lenses are relics of an era when Barlows featured weaker lenses, allowing for greater tolerance of optical defects but having clearance issues on some diagonals or focusers. Nonetheless, they remain an excellent, if not exactly cheap, choice. Tele-Vue presently offers 2x and 3x units, but 1.8x and 2.5x Barlows can also be found on the used market.

5. Best $200+ Choice: Tele Vue 2.5X Powermate

Tele Vue 2.5x - 1.25" Powermate - PMT-2513
Instead of the common divergent ray design typical of Barlow lenses, the Tele-Vue Powermate uses a telecentric optical structure. The 2.5x Powermate is great for both visual and imaging purposes, while the 5x is really exclusively designed for planetary imagers.

6. Second Best $200+ Choice: Explore Scientific 1.25” Focal Extender

Explore Scientific 1.25" 2x Focal Extender
The Explore Scientific Focal Extenders use a unique telecentric design like the Tele-Vue Powermate, which means that the magnification/focal length change won’t differ based on the spacing of your eyepiece or camera from the lens element. The focal plane is also not shifted much by these devices. Explore Scientific offers 2x, 3x, and 5x 1.25” focal extenders for you to choose from. These devices used to be priced lower than their Tele-Vue equivalent, but as of 2023, the price difference is so thin that we would urge you to just get the higher-quality Powermate unless you absolutely need 2x or 3x and not 2.5x.

Best Barlow Lens For 2″ Focuser: My Recommendations

Combining a 2” Barlow lens with a 2” eyepiece can add significant weight to the telescope setup. This combination might introduce balance issues, which can affect the stability and orientation of your telescope. Always ensure that your telescope can comfortably support the combined weight of the Barlow lens and the eyepiece to avoid any mishaps.

A 2” Barlow is unnecessary for most users, as a Barlow generally is only needed to extend magnifications to higher than your eyepieces allow, where you are likely to be using 1.25” eyepieces towards the higher-power end anyway. Likewise, for planetary imaging, any suitable camera sensor does not need a 2” Barlow.

1. Under $100: GSO 2″ 2x ED

GSO 2" 2x ED Barlow Lens # GS22B
This Barlow Lens is a real bargain. It will accept 2” and 1.25” eyepieces, allowing you to add a second magnification option for both sizes of eyepieces. GSO’s 2” Barlow (also available under the Apertura brand name) features a two-element lens with an ED glass element, which can help maintain image quality. It also has a removable Barlow element that can be screwed directly onto a 2” eyepiece for 1.5X, giving you an additional magnification option. If you want a low-cost 2” Barlow to extend your 2” and 1.25” eyepieces, this is the one to get.

2. Between $100 – $175: Celestron Luminous 2” 2.5X Barlow Lens

Celestron 2" 2.5x Luminos Barlow Lens # 93436
The Celestron Luminos 2.5x Barlow Lens features a 4-element lens with ED glass (permanently affixed inside the body). Unsurprisingly, this leads to a heavy but compact unit. However, if you don’t mind the weight or price, this Barlow puts up remarkably sharp images. The 2.5X multiplication allows you to space your magnifications a little differently than a 2X or a 3X. For some, 2.5X might be the better choice.

3. Between $175 – $250: Explore Scientific 2” 2X Focal Extender

Explore Scientific 2" 2x Focal Extender - FE02-020
A focal extender is based on a slightly different design from a true Barlow lens but serves the same purpose, adding multiplication options for your eyepieces. Explore Scientific has the reputation of offering a higher-quality build and delivering a better experience, but at a higher price. If you are going to go for higher-priced eyepieces, this might be a better choice. Available in 2x and 3x configurations, the Explore Scientific 2” Focal Extenders offer the same design and features as their 1.25” counterparts, with a telecentric design minimizing changes to focus or amplification from spacing and featuring a brass compression ring to grip your eyepieces.

4. $275+ Choice: Tele Vue 2X 2” Powermate

Tele Vue 2.0x - 2" Powermate - PMT-2200
Tele Vue is one of the top names in astronomy optics. The Powermate is optically a little different as it is based on a telecentric optical design, whereas a Barlow lens is based on a divergent ray design. Meaning that there is no difference in amplification if your eyepiece or camera’s spacing from the lens is different, and the focal plane does not shift appreciably either. That being said, they are used in the same way. If you must have the highest-quality image to support your top-of-the line eyepieces, this is the one to get.

Advantages and Disadvantages of Barlow Lenses

  • Enhanced Eye Relief: One of the standout benefits of using a Barlow lens is the ability to maximize eye relief. Eye relief denotes the optimal distance your eye needs to be from the eyepiece’s top lens to capture the entire field of view. Longer focal length eyepieces, which inherently possess lower power, often grant longer eye relief. This is pivotal for ensuring a comfortable viewing experience.
  • Economical: Instead of purchasing multiple eyepieces for varied magnifications, a single Barlow lens can multiply the effective magnifications of eyepieces you already possess.
  • Potential Image Quality Loss: Introducing an additional optical component into the light path might lead to a significant loss of sharpness or contrast if the Barlow isn’t of high quality.
  • Focus shift: Barlow lenses that don’t properly seat in your focuser or diagonal body due to their length or other constraints can move the focal plane of the telescope so far that it is no longer possible to focus the image at the eyepiece.
  • Weight: A 2” Barlow lens in particular is likely to throw off the balance of many telescope setups, and a Barlow inevitably leads to more strain on your focuser as the eyepiece is further from the focuser body, exerting more torque in addition to the eyepiece itself. This can cause cheaper focusers to sag or rack themselves up on their own.

9 thoughts on “Best Barlow Lenses For Your Telescope”

  1. The goal of the article is not to do a competitive comparison between barlows.

    As far as 1.25″ vs. 2″, the main consideration is whether you have 2″ eyepieces and whether you want to barlow them. Most people don’t barlow 2″ eyepieces.

    I have a 2″ 2X GSO barlow that I like very much, but I don’t use it as much as I thought I would. When I didn’t have wide angle 1.25″ eyepieces I used it for a while, but as I filled in my eyepiece set with 82 degree 1.25″ eyepieces I stopped using the 2″ barlow. But, for a while, I used it a lot.

    Most people have one or two 2″ eyepieces and the rest are 1.25″. The exception may be those people who have very long focal length scopes, say over 3000 mm, who would like to leverage their 2″ eyepieces and their wide apparent field of views. 2″ eyepieces tend to be quite expensive so being able to barlow them can be a very reasonable approach if your eyepiece budget is limited.

    One of the scopes I use is a 14″ Meade LX200 with a 3500 mm FL. I have two 2″ eyepieces. I could use my 2″ barlow with this one, but find I tend to go to my 1.25″ 82 degree eyepieces rather than barlow the 2″ eyepieces.

  2. Ed, Thanks. I do understand that the point of the article was to compare barlows, sorry I didn’t mean to go off on a tangent. It’s just that I see lots of reviews on different equipment and barlows is one I have not seen.

    Regardless, going back to your comment regarding 1.2″ vs. 2″. I assume that while there may be limited use for a 2″ barlow that as long as you have a 1.25″ adaptor there is no harm in a 2″?

    • As is described in the article, you pick your Barlow according to your goals. What level of magnification are you trying to achieve and what eyepieces you have now. However, I have found that GSO makes good, moderate-priced barlows. I have two and like them very much.

      With a 70 mm aperture, I would not look to push more than 140X with any expectation of a good image. Much of the time 100X will probably give you a better image with more detail. But don’t hold back on my say so. A Barlow is a great, inexpensive way to test those higher magnifications without having to buy eyepieces. Some nights the air will let you push much higher than you can normally.

  3. Hi there. In the comments for your article on eyepieces you mention that you use a 2x Barlow with your BHZ eyepiece that has a removable element also making it a 1.5x. Is this the GSO Barlow mentioned in this article and if so, is it the 2″ or 1.25″ version? Many thanks.

    • The 2X Barlow I use with the Baader Hyperion Zoom is the 2″ GSO which has a removable 1.5X Barlow lens. I screw this onto the 1.25 to 2″ adapter that comes with the zoom which is treaded for filters. This works very well in my 8″ and 12″ Newtonian/Dobsonians as I would need an adapter for the BH Zoom in these focusers. However, GSO has the 1.25″ version that can be used directly on the zoom and would be most appropriate for a 1.25″ focuser scope. I have not used the 1.25″ GSO but have no doubt it would work well.

      If you use this method in a diagonal, check to make sure that the added length of the Barlow element does not touch the mirror/prism in the diagonal. If it would touch you might have to pull back a bit and lock the zoom there. You can also buy parfocalizing rings that lock onto an eyepiece barrel to hold it out of the focuser a bit on a consistent basis. Just make sure that if you use the zoom without the Barlow element that you have enough into the diagonal to get a solid lock on the eyepiece. This is not a concern on a Newtonian as there is no diagonal.


Leave a Comment