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GSO 1.25" 90-deg Mirror Star Diagonal for Refractors # GSST

4.7 (21 Reviews) Read Reviews Write Review
Brand GSO
Part Number GSST
Availability available

Product Info

Manufacturer Description

GSO's 90-deg mirror diagonal is a very good, economical replacement for the generic diagonal that probably came with your otherwise fine scope. Features Al+SiO2 coatings with 92% reflectivity across the visible spectrum and a 1/10 wave mirror.

The clear aperture is 27.9mm. The main mirror housing is made of precision molded ABS plastic and the two end barrels are precision machined from aluminum. The 1.25" nosepiece is threaded to accept standard 1.25" astronomy filters. Weight: 4.4oz; 2 end caps included. Made in Taiwan.

Please Note: This diagonal can only be used with refractor telescopes and some catadioptric telescopes like Schmidt-Cassegrain, Maksutov-Cassegrain, etc. It not meant for use with Newtonian / Dobsonian reflector telescopes or other variants of Newtonian telescopes.

Reviews

4.7 (Based on 21 Reviews) 100% of reviewers recommended this product.
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    1. Guest

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      Review by Jim Z.
      1546831990
      Jan 6, 2019

      5.0 GSO Star Diagonal 1.25"

      Pros:

      Cons:

      Comments:

      Purchased it when it was on sale for $27. What a bargain, well built and high light reflectivity. Agena Astro ships fast and it's free.


      Top notch service and free shipping. Agena Astro can't be beat. This star diagonal I purchased for $27 on sale is typical of their quality.

      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 Michael Z.
      1529419727
      Jun 19, 2018

      5.0 Great item at a great

      Pros:

      Cons:

      Comments:

      Great item at a great price.

      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 Brad Bowles
      1518563214
      Feb 13, 2018

      5.0 Awesome Value

      Pros:

      Cons:

      Comments:

      I have always had good luck with GSO products. They make a quality product at all levels for a fair price. This diagonal has a plastic body and metal barrels. I actually wanted something lighter to use with my 80mm Short Tube refractor. There is not any front to back adjustment on my scope so I wanted to keep the off balance condition a small as possible on my photo tripod. A full metal body diagonal would have put too much weight to the rear of the scope. This diagonal is much better for astronomical use over the Amici roof prism diagonal that came with my scope. You can spend twice as much on a diagonal but I doubt you will get twice the performance.

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

      This review was provided courtesy of AgenaAstro.com

    4. Guest

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      Review by Greg D.
      1505483825
      Sep 15, 2017

      5.0 Good diagonal

      Pros:

      Cons:

      Comments:

      Nice diagonal much better than prism that came with my inexpensive scope

      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 cody c.
      1505276810
      Sep 12, 2017

      5.0 Very good pice

      Pros:

      Cons:

      Comments:

      I have use it now for two weeks and no problems with it very good quality

      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 Roger B.
      1504800894
      Sep 7, 2017

      4.0 Nice diagonal

      Pros:

      Cons:

      Comments:

      Nice price, good construction, nice performance. Feels better than stock a diagonal as well. Recommended.

      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 Matt C.
      1502036008
      Aug 6, 2017

      4.0 The diagonal arrived quickly and

      Pros:

      Cons:

      Comments:

      The diagonal arrived quickly and exceeded expectations.

      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 K.D.
      1484743423
      Jan 18, 2017

      5.0 A solid diagonal!

      Pros:

      Cons:

      Comments:

      Way better than the junk 45 degree diagonal that comes with the C90. Views are generally sharper, and the views are substantially better.

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

      This review was provided courtesy of AgenaAstro.com

    9. JoeinWV

      JoeinWV New Member

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      Review by Joseph M.
      1484191880
      Jan 11, 2017

      5.0 GSO diagonal

      Pros:

      Cons:

      Comments:

      Exactly as described. Well made, great price.
      Bought for a C-90 and fits perfect.

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

      This review was provided courtesy of AgenaAstro.com

    10. Guest

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      Review by Abreu M.
      1483532246
      Jan 4, 2017

      5.0 Incredible Quality

      Pros:

      Cons:

      Comments:

      This diagonal is better than the ones that come when we buy a telescope

      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 Dude of California.
      1476316800
      Oct 12, 2016

      5.0 Great upgrade for my scope

      Pros:

      Strong Construction,Accurate,Lightweight,Easy to Use

      Cons:

      Comments:

      This is a great upgrade for my scope. The cheap plastic diagonal that came with my scope had stripped set screw threads. The GSO diagonal is made of metal and feels much stronger. Made of metal, but it's still light weight. It can support heavier eyepieces than the old plastic one. The mirror is good quality. The field of view is wider than my original diagonal too. Very good quality for this low price. I'm happy.

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

      This review was provided courtesy of AgenaAstro.com

    12. Guest

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      Review by chrome of Cedaredge, Colorado.
      1453766400
      Jan 25, 2016

      4.0 Very nice low cost star diagonal.

      Pros:

      Strong Construction,Lightweight,Quality Lenses,Easy to Use,Accurate

      Cons:

      Comments:

      I have not used this much. I will be using it with an off-axis guider and I am still working on that. Winter has slowed the process. But I think it will be fine.

      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 JQE of Vancouver, WA.
      1444435200
      Oct 9, 2015

      5.0 Fantastic for the price

      Pros:

      Easy to Use,Quality Lenses,Strong Construction

      Cons:

      Comments:

      I bought this diagonal to replace a 45-degree prism that came with my C90. It presents a nice, clear image. The case is made of actual metal as well, and is very sturdy without being unnecessarily heavy. It feels like a diagonal that's worth twice the price!

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

      This review was provided courtesy of AgenaAstro.com

    14. Dr. Ski

      Dr. Ski Well-Known Member

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      Review by Dr. Ski of Obscure Philippine island.
      1439164800
      Aug 9, 2015

      5.0 Incredible

      Pros:

      Accurate,Lightweight

      Cons:

      Comments:

      If your scope came with a prism diagonal, you need to replace it ASAP with this surprisingly good, cheap accessory. It's that simple!

      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 Wes of Texarkana, AR.
      1423008000
      Feb 3, 2015

      5.0 A Pleasant Surprise

      Pros:

      Collimated Well,Lightweight,Easy to Use

      Cons:

      Comments:

      I bought this diagonal to replace the terrestrial diagonal that came with my 80mm Celestron refractor. I have used it with up to 240X and the image quality has no breakdown that I can see. It is also well collimated, giving symmetrical Airy Discs of point light sources (stars and reflections from the sun). I am very pleased with it.

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

      This review was provided courtesy of AgenaAstro.com

    16. Guest

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      Review by Michael of Athol, Idaho.
      1360368000
      Feb 8, 2013

      5.0 Great Diagonal

      Pros:

      Strong Construction,Lightweight

      Cons:

      Comments:

      I was sceptical about this low cost digonal. But other reviews encouraged me to take a chance on it. I'm glad I did. This diagonal is great. The mirrors are clear and the views are excellent. The low cost is nothing to be afraid of. You definetly get a great diagonal for the price. I use it in my 80mm piggyback refractor so someone else can look at the night sky without having to wait for the eyepiece to become free on the reflector. It is machined precisely and fits the tube and eyepieces perfectly.

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

      This review was provided courtesy of AgenaAstro.com

    17. Nubcaek

      Nubcaek New Member

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      Review by Herp McDerp of Bellflower, CA.
      1274227200
      May 18, 2010

      4.0 Galileoscope+barlow lens=usable diagonal

      Pros:

      Compact,Strong Construction,Accurate

      Cons:

      Comments:

      I bought this and the GSO 2x shorty barlow and put the barlow lens element on the front of this to reach focus with a diagonal on a Galileoscope.

      Yes you can get 3 Galileoscopes for the combined price but I would assume anyone getting a Galileoscope would want to upgrade to something larger in the future. This diagonal looks good and didn't add any visible problems to me.

      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 twidds of Lincoln, UK.
      1243555200
      May 28, 2009

      5.0 A shining example to others

      Pros:

      Strong Construction,Accurate,Quality Lenses,Compact

      Cons:

      Comments:

      Excellent product

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

      This review was provided courtesy of AgenaAstro.com

    19. Guest

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      Review by elias of Athens, Greece.
      1243382400
      May 26, 2009

      4.0 Excellent value

      Pros:

      Compact

      Cons:

      Plastic body

      Comments:

      Using my 2" diagonal and 2" bulky and heavy accessories with my ED80 is the norm. However, I wanted to be able to use the scope for a quick look or on grab-and-go occasions. Using a light 1.25" diagonal with a couple of 1.25" eyepieces and a barlow seemed like a good idea. The GSO 1.25" diagonal proved to be the perfect accessory for the job.

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

      This review was provided courtesy of AgenaAstro.com

    20. Guest

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      Review by Vergil of Germany.
      1243382400
      May 26, 2009

      4.0 Good quality

      Pros:

      Accurate

      Cons:

      Comments:

      Was very happy with item

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

      This review was provided courtesy of AgenaAstro.com

    21. Guest

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      Review by mhuston6 of Florida.
      1227830400
      Nov 27, 2008

      5.0 GSO 1.25" 90

      Pros:

      Fine optics,Good buy,Light weight

      Cons:

      No bad reviews

      Comments:

      This 90* is much better than the one that comes with your OEM refractor!! The images are more clear and it is about the same weight! The price is one of the best features for me!! All-round nice accessory!!

      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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      Specifications

      Manufacturer GSO