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GSO 1.25" 5x Apochromatic Barlow Lens # BL501

4.3 (18 Reviews) Read Reviews Write Review
Brand GSO
Part Number BL501
Availability available

Product Info

Manufacturer Description

If you need more power than your eyepieces alone can provide, we offer a new apochromatic 5x Barlow lens from GSO (Guan Sheng Optical) to give a big magnification boost to any 1.25" eyepiece it's used with.

Nothing has been compromised in GSO's latest and finest offering. This Barlow features an air-spaced, three-element, apo design with fully multicoated optics. The housing is precision machined from aluminum stock and black anodized to a hard finish. The lens edges and inner barrel are blackened to provide maximum contrast. The Barlow body includes a safety undercut on the lower barrel and a brass compression ring so that your eyepiece barrels are not marred by the captive set screw. The 5x model has a clear aperture of 13mm, but it is not threaded to accept 1.25" filters.

For those blessed with great optics and dark skies, the 5x could be an exciting new addition to your arsenal for visual and photographic use. If you've never used such a powerful barlow before, please be aware that to get the best out of this barlow, you need to use it with a good telescope, a good eyepiece and under good seeing conditions. See more on this topic below.

Specifications:

  • Barrel size = 1.25" (31.7mm)
  • Magnification factor = 5x
  • Weight = 3.8oz (108gm)
  • Total height = 3.46" (88mm)
  • End caps = 2
  • 1.25" filter threads on bottom of barlow: No
  • Made in Taiwan

Please note: This is a very high magnification barlow. It is not for everyone or for common viewing conditions. Before buying, please make sure that you are using realistic magnifications with your telescope. A good rule of thumb is that under very good conditions and with a very good telescope, the maximum power you will be able to use is about 50x of magnification per inch of telescope aperture. With average telescopes and/or average conditions, you should be able to use 30x of magnification per inch of telescope aperture. So for example, if you have a 6" telescope, under typical conditions you will be limited to 6x30 = 180x of magnification, and 6x50 = 300x of magnification at best.

Boosting the magnification beyond this recommended maximum for your telescope aperture is not realistic. This is bound to result in image break-down, causing fuzzy images, focusing difficulties, increased color around objects (caused by other optical elements in the telescope which are magnified by the barlow) and general disappointment, but this is not a fault of the barlow.

Reviews

4.3 (Based on 18 Reviews) 83% of reviewers recommended this product.
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    1. Guest

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      Review by Geethika S.
      1525635949
      May 6, 2018

      4.0 good price vs performace

      Pros:

      Cons:

      Comments:

      overall its good for the money. i have used it with my 8" Newtonian for planets. yet to try it for planetary AP. i also have the GSO ED 3X Barlow and it performs better than this in same magnification.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    2. Guest

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      Review by Adrian 0.
      1503835652
      Aug 27, 2017

      5.0 Great barlow!

      Pros:

      Cons:

      Comments:

      Nice equipment at the perfect price! great addition to any astronomy kit.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    3. Guest

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      Review by Nordmandpc of Sao Luis, MA, Brasil.
      1409961600
      Sep 5, 2014

      5.0 I recommend

      Pros:

      Lightweight,Easy to Use,Strong Construction,Quality Lenses

      Cons:

      Comments:

      It's a good product and it's exactly what the website announced.

      Bottom Line: Would you recommend this item? No
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    4. Guest

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      Review by superdude68 of Runcorn,England.
      1402704000
      Jun 13, 2014

      3.0 Wow So Close

      Pros:

      Compact,Easy to Use,Strong Construction

      Cons:

      Difficult To Focus

      Comments:

      On my CPC 800 I find the use of the GSO 1.25" 5x Apochromatic Barlow Lens very hard to focus. Don't get me wrong, it's still good for getting close to things if you are just looking. Maybe its my lenses because there not so great, still on the cheap ones.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    5. Guest

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      Review by skaven of San Diego, CA.
      1369958400
      May 30, 2013

      4.0 Great quality, but a niche product

      Pros:

      Easy to Use,Strong Construction,Compact

      Cons:

      Difficult To Focus

      Comments:

      I purchased this barlow to use with a webcam CCD in my 10" f/4.7 scope for planetary imaging. With the 5x barlow it bumps the scope up to f/24, which is closer to where I need to be for planetary imaging with a CCD.

      The complexities of aiming, aligning, and focusing a 10" f/24 scope aside, I found that this barlow did very well. Once focused, the image stayed sharp across the field and had even illumination.

      However, I was a bit disappointed by the chromatic performance. While billed as an apochromatic barlow, I found that there was noticeable blue fringing around bright targets. All other colors, however, were kept well in check.

      This barlow also has a problem with dust motes. Due to the high power of the lens, your camera comes to focus with the barlow's objective lens a hair's width below the primary mirror's focal plane. The result is that any foreign material on the barlow's objective lens is visible in your CCD image. Great care must be taken to have pristine lens surfaces to prevent this effect.

      In all, I am happy with my purchase. But for those interested in it, do keep in mind that this barlow packs a LOT of power, and will very easily overpower your scope if used visually. It will be basically unusable in an f/10 SCT for both visual and camera work, as it will magnify well beyond the diffraction limit of the scope. It's best used in fast (f/4-f/6) scopes to "convert" them into slower scopes for planetary imaging.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    6. Guest

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      Review by George72 of Rubi, Spain.
      1335830400
      Apr 30, 2012

      4.0 Absolutely perfect!!!

      Pros:

      Strong Construction,Accurate,Quality Lenses

      Cons:

      Difficult To Focus

      Comments:

      Very good item but difficult use about his magnification (x5), I only can use with a very good weather conditions.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    7. Guest

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      Review by Jeudy of Costa Rica.
      1323648000
      Dec 11, 2011

      4.0 Good and afordable barlow

      Pros:

      Lightweight,Compact,Strong Construction,Quality Lenses

      Cons:

      Comments:

      Very nice for its price. Looks strong and lenses quality looks fine.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    8. Guest

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      Review by chris of Ile-de-france, France.
      1319932800
      Oct 29, 2011

      5.0 I would buy this product again

      Pros:

      Quality Lenses,Strong Construction

      Cons:

      Comments:

      I use it for the collimation and for the solar system photo with a refractor ed100 / 900.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    9. Guest

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      Review by Almir of Brazil.
      1319846400
      Oct 28, 2011

      2.0 Not as good as I thought

      Pros:

      Cons:

      Poor Lens Quality,Difficult To Focus

      Comments:

      Meh... So far I could not get a good impression of it. Difficult to focus, the lens quality does not seems very good, the field looks much more dark than with my Powermate 2.5X.

      Bottom Line: Would you recommend this item? No
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    10. sebagr

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      Review by Sebastian of Buenos Aires, Argentina.
      1307404800
      Jun 6, 2011

      4.0 Does its job

      Pros:

      Strong Construction,Accurate

      Cons:

      Comments:

      At first, I received a defective unit, but guys from Agena replaced it and it works like a charm now.

      Granted, this is not a Powermate, but it does its job. I couldn't see any noticeable chromatic aberration and it worked great while coupled with several different eyepieces.

      I'd definitely buy it again.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    11. Guest

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      Review by Volkano Viktor of Sao Paulo, Brazil.
      1292889600
      Dec 20, 2010

      5.0 Best for the price

      Pros:

      Accurate,Strong Construction,Quality Lenses,Premium quality,Compact

      Cons:

      Comments:

      This is the best you can get for this price. Very high quality

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

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      Review by Too Tall Tony of St Clair Shores, MI.
      1292803200
      Dec 19, 2010

      4.0 Great barlow for a great price

      Pros:

      Strong Construction,Quality Lenses,Accurate

      Cons:

      Comments:

      I use this all the time as a planetary webcam magnifier, and for collimating my SCT, which has a short [1600mm] focal length, so I need a lot of help getting the high power needed for collimating ,while still using a lens that's bright enough to still make the star stand out. With this barlow I have no problems getting the concentric rings to show up enough for accurate work.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    13. Guest

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      Review by Fco of Argentina.
      1274140800
      May 17, 2010

      5.0 Good value for money

      Pros:

      Accurate,Quality Lenses,Strong Construction,Compact

      Cons:

      Comments:

      The Barlow 5x is a great tool for my short focal distance reflector telescope, which allows me to get better views of planets...

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    14. Guest

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      Review by William of Newburg, MD.
      1273276800
      May 7, 2010

      5.0 Preimum barlow

      Pros:

      Quality Lenses,Excellent finish,Accurate,Strong Construction,Compact

      Cons:

      Comments:

      I purchased this to use for planetary video and when seeing is good it is excellent. Also use it on my SV80S and it works great with very sharp images. The quality is excellent, which I find unusual today.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    15. Guest

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      Review by Lerros1978 of Cologne, Germany.
      1243468800
      May 27, 2009

      4.0 I would buy this product again

      Pros:

      Strong Construction,Quality Lenses,Accurate

      Cons:

      Difficult To Focus

      Comments:

      The quality of this product is really good if you got to think about the price. I am using it to take pictures of the planets via webcam. That the focusing is not really easy is absolutely normal if you know that the optical chip in a webcam is very small. The TeleVue`s Powermate will be always better, but you got to pay four times more than this. I would buy it again!

      Bottom Line: Would you recommend this item? No
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    16. Guest

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      Review by malenkov of Alicante Espana.
      1243468800
      May 27, 2009

      5.0 I would buy this product again

      Pros:

      Cons:

      Comments:

      Excellent

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    17. Guest

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      Review by Mo of South Dakota.
      1243468800
      May 27, 2009

      5.0 Great lens, perfect fit, love the view

      Pros:

      Quality Lenses,Accurate,Compact,Strong Construction

      Cons:

      Comments:

      Couldn't be happier with it.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

    18. Guest

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      Review by Starwolf of Glenside, PA.
      1235088000
      Feb 19, 2009

      5.0 An excellent buy at an affordable price!

      Pros:

      Strong Construction,Compact,Quality Lenses,Accurate

      Cons:

      Comments:

      I bought this barlow shortly before the opposition of Mars in December of '07. The views through my 10" reflector were surprisingly crisp, even though I surpassed the power rule of 50x per inch of aperature. Another great feature is the fact that it uses a compression ring which gives uniform snugness as compared to a setscrew which tends to mar the collar of the eyepiece. All in all a great buy. Thanks guys.

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

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