Dismiss Notice
New Cookie Policy
On May 24, 2018, we published revised versions of our Terms and Rules and Cookie Policy. Your use of AstronomyConnect.com’s services is subject to these revised terms.

More Views

GSO 0.965"/1.25" 90-deg Hybrid Erect-Image Prism Diagonal

4.0 (6 Reviews) Read Reviews Write Review
Brand GSO
Part Number ODIA-GS-PD90-HYBRID
Availability available

Product Info

Manufacturer Description

Important Note: Please note that the length of the 0.965" nosepiece, as listed below, is 15mm (0.59"). Before purchase, please make sure that the thumbscrew on your telescope is within this distance from the rear end of your focuser drawtube. Otherwise, the thumbscrew will not be able to engage and lock the diagonal. This is a known issue with some vintage telescopes in which the locking thumbscrew on the telescope is recessed by more than 0.6", and this diagonal will not work for you.

Disappointed by the lack of quality 0.965" eyepieces for your vintage telescope? Missing a diagonal for that small telescope you picked up in a garage sale? Wish you could use wider angle 1.25" eyepieces with your small spotting scope? Here's the solution you need!

Many vintage telescopes sold up to the 1960s, cheap introductory telescopes sold today, and many spotting scopes use a smaller, older, almost obsolete 0.965" diameter format for diagonals and eyepieces. Having a 0.965" barrel severely limits the number of eyepieces and accessories you can buy and use in the after-market.

This popular hybrid diagonal from GSO allows 1.25" eyepieces, diagonals, and other accessories to be used in 0.965" focusers, and at once allows hundreds of more common 1.25" format astronomy items to be used with your telescope.

GSO's hybrid 0.965"-1.25" 90-degree diagonal features an image erecting Amici glass prism that allows you to look into a telescope at a 90 degree angle. It produces an image that is oriented properly, which means that the image is upright and correct from left to right (i.e., a correct, non-inverted, non-reversed image). This is a great diagonal for daytime terrestrial use with small telescopes or spotting scopes. It can also be used for nighttime astronomy applications, especially when you would like to match the orientation of the star field with "correct" star maps and charts.

A unique feature of this hybrid diagonal is the use of a dual step 0.965"/1.25" chrome barrel on the telescope end. While designed primarily for use with 0.965" focusers, the step barrel also allows you to use this diagonal in 1.25" focusers (although your field of view might vignette in some situations if used in this manner). Total length of the nosepiece is 25mm (0.98"); length of 1.25" portion of nosepiece = 10mm (0.39"); length of 0.965" portion of nosepiece = 15mm (0.59").

The prism housing is made of high grade ABS plastic and the end barrels are made from precision machined aluminum. Weight: 3.7oz; 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

4.0 (Based on 6 Reviews) 67% of reviewers recommended this product.
Rating Distribution
Sort by
  • Date
  • Rating
  • Useful
    1. Guest

      Skill Level
      Unknown
      Time with Product
      Unknown
      User Notes:
      Review by Yvon B.
      1503281884
      Aug 20, 2017

      4.0 Worked perfectly!

      Pros:

      Cons:

      Comments:

      Worked perfectly!

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

      This review was provided courtesy of AgenaAstro.com

    2. Guest

      Skill Level
      Unknown
      Time with Product
      Unknown
      User Notes:
      Review by Thom of Minerva, OH.
      1455062400
      Feb 9, 2016

      4.0 I like the product, would buy again.

      Pros:

      Lightweight,Strong Construction,Easy to Use,Quality Lenses

      Cons:

      Comments:

      I use this with a 90 mm spotting scope with excellent results.

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

      This review was provided courtesy of AgenaAstro.com

    3. Guest

      Skill Level
      Unknown
      Time with Product
      Unknown
      User Notes:
      Review by craterdavy of Maine.
      1427673600
      Mar 29, 2015

      3.0 You get what you pay for

      Pros:

      Quality Lenses,Lightweight

      Cons:

      Comments:

      The optics seem good.,,but the .965 barrel is short.,,and a little to skinny.,,not a good fit.

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

      This review was provided courtesy of AgenaAstro.com

    4. Guest

      Skill Level
      Unknown
      Time with Product
      Unknown
      User Notes:
      Review by worcspaul of Worcestershire UK.
      1410048000
      Sep 6, 2014

      4.0 A little more machining required

      Pros:

      Strong Construction,Accurate,Easy to Use

      Cons:

      Difficult To Focus

      Comments:

      I bought this to use with an old 60mm refractor which has 0.965" fittings. The diagonal is well made with a good, strong 0.965" nosepiece. However, I am unable to reach focus as the thick "collar" at the base of the 0.965" section causes an attached 1.25" eyepiece or webcam to be too far back - even with focus wound right in. I'm sure a reduction of the collar to a 1-2mm thickness would be sufficient to correct this.

      If it hadn't been for this I'd have given it a five star rating. I would only recommend to a friend if the focus issue were to be resolved

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

      This review was provided courtesy of AgenaAstro.com

    5. Guest

      Skill Level
      Unknown
      Time with Product
      Unknown
      User Notes:
      Review by Telescope Tim of East Coast USA.
      1403049600
      Jun 17, 2014

      4.0 Performs well, but may have to collimate

      Pros:

      Easy to Use

      Cons:

      Comments:

      I use this diagonal in a 1960's 3" F16 refractor. It's nice to be able to use 1.25" eyepieces in the old scope without additional adapters. The more adapters you have, the greater the chance of misalignment from eyepiece to objective. This is a superior remedy.

      One issue that I did find was that the mirror was not collimated well from the factory. I found it to be significantly off. In my F16, this may not be much of a big deal, but I collimated it anyway by loosening the four screws on the outside of the backplate and inserting folded pieces of foil between the plate and housing. I then tightened the screws appropriately until I was well collimated.

      I find the surface to be well polished / accurate. No problems viewing fine planetary detail and splitting tight double stars. Izar looks nicer in this diagonal than it does in my OEM prism. I also have a slightly better view of Cassini's division with this diagonal than the OEM prism.

      Also, the aluminum coating is just fine. Contrast is not quite up to the level of my prism diagonal, but it's very good and does not introduce false color like a prism diagonal may. Light scatter is decently controlled as well. I did compare this with an older Televue mirror diagonal I have (the one that came with the old TV Ranger) and would say they are on par with each other after you collimate the GSO.

      All in all....for the price (and if you can collimate)...I'd recommend.

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

      This review was provided courtesy of AgenaAstro.com

    6. Guest

      Skill Level
      Unknown
      Time with Product
      Unknown
      User Notes:
      Review by John V. of Oshawa, Canada.
      1370304000
      Jun 3, 2013

      5.0 Great for old 0.965 telescope

      Pros:

      Strong Construction

      Cons:

      Comments:

      Put's life back into old telescope.

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

      This review was provided courtesy of AgenaAstro.com

    Sort by
    • Date
    • Rating
    • Useful

      Specifications

      Manufacturer GSO