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GSO 1.25" 0.5x Focal Reducer
| Brand | GSO |
| Part Number | GSRD |
| Availability | available |
| Share |
Product Info
Manufacturer Description
GSO's popular 1.25" 0.5x focal reducer screws on to any accessory such as eyepieces, camera adapters, etc. that accepts standard 1.25" threaded filters and provides a nominal reduction of 0.5x. Use of this focal reducer effectively halves the focal ratio of your telescope, resulting in a wider field of view and significantly shortened exposure times for astrophotography. For example, use of this reducer will convert an f/10 telescope into an f/5 scope.
The 2-element reducer features fully multi-coated optics in a black-anodized aluminum filter cell. It also has additional 1.25" female threads so you can screw/stack additional 1.25" filters on to this reducer. This focal reducer will work well for visual use too when coupled with the right kind of eyepieces and telescopes; it is not recommended for very fast scopes or very wide angle eyepieces for visual applications.
Note that the use of any optical element like barlows and focal reducers changes the focus point of your telescope, requiring additional in-focus or out-focus travel. The exact amount of focus travel required will depend on the optics and mechanics of your specific set-up (telescope, diagonal (if used), barlow/reducer, and eyepiece). Hence, be aware that you may not be able to reach focus with all eyepieces or in all configurations with a given barlow/reducer. In our tests, when screwed into an eyepiece, this focal reducer required approximately 8mm of additional in-focus travel so please make sure that your focuser can accommodate this travel requirement.
Specifications:
- Focal length (estimated) = 101 - 103mm (3.98 - 4.06")
- Total item length (including external thread) = 13mm (0.51")
- Total item length (excluding external thread) = 10mm (0.39")
- Clear aperture = 22mm (0.87")
- Weight = 0.5 oz.
- Made in Taiwan
Varying the Reduction Factor of a Focal Reducer
The actual reduction will vary a little over or under 0.5x depending on exactly where the focal reducer is placed in the optical path. The exact focal length specification of this reducer has not been provided by the manufacturer, but we estimate it to be approximately 101-103mm. Hence, the "working distance" of this specific reducer is estimated to be 51mm, i.e., this reducer will provide a reduction of 0.5x when the center of its lens assembly is placed 51mm from the focal plane of the eyepiece or imaging device. Move the focal reducer closer to the eyepiece/camera and its reduction factor will increase. Move it away and the reduction provided will decrease.
By using additional spacers or extension tubes (sold separately), you can vary the amount of reduction you obtain with this reducer as follows:
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Extra Spacer Length
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Nominal Reduction Provided
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0" / 0mm
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0.50x
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0.25" / 6.4mm
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0.44x
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0.5" / 12.7mm
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0.38x
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0.75" / 19.1mm
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0.31x
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1" / 25.4mm
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0.25x
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However, do not be tempted to buy only the longest spacer tube to get the most reduction. A focal reducer will provide good results as long as it is placed "close" to its working distance. For example, it is possible that a 0.5" spacer will provide good results, a 0.75" spacer will provide acceptable results, and a 1" spacer might be unacceptable for your telescope/eyepiece combination. You will usually have to determine this by trial and error for your set-up, so you might want to consider buying more than one spacer.
Reviews
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Jun 28, 2019
Exactly what I was looking
Pros: Cons: Comments:Exactly what I was looking for at a good price. Used it to fit a bit more of the moon in the frame - Celestron 127 Mak, ASI224mc.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Jun 29, 2018Not for Lower Power Eyepieces
Pros: Cons: Comments:I found the GSO .5 reducer to be well made, with good coatings and light throughput. However, while it performed as advertised in mid-focal length eyepieces, it produced significant vignetting on my 24mm and 30mm. The result was a lower magnification, but no significant gain in FOV - which is the whole point of using a reducer visually. I tried a number of placements in my 8" SCT, but could not obtain satisfactory views.
Bottom Line: Would you recommend this item? Yes
To Agena's credit, they accepted my return and issued a full refund.This review was provided courtesy of AgenaAstro.com
Sep 15, 2017Funtional optics
Pros: Cons: Comments:I ordered this magnification reducer because I couldn't get lenses for my 102 mm Maksutov Cassegrain telescope that would pull the entire sun into view for the eclipse. I needed to reduce the effective focal length of the telescope so I could get the full benefit of seeing the solar prominences all around the moon during totality. It worked perfectly for my purpose.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Aug 20, 2017Great quality and service
Pros: Cons: Comments:Impressed with the quality of the product but I had to return it as it didn't match my telescope. Impressed with the response from the customer service and quick refund.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Jul 1, 2017GSO Focal Reducer
Pros: Cons: Comments:Absolute first rate. The reducer appears to be high quality, nice coated lenses, and works as it should. The shipping was extremely fast!! I will check for availability at Agena first from now on when I need any telescope part.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Apr 25, 2017Works as advertised
Pros: Cons: Comments:Using with my C11 EdgeHD SCT both for visual and astrophotography. Solid piece of equipment and easy to attach.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Feb 17, 2017Works like a charm.
Pros: Cons: Comments:I use this to increase FOV when imaging the solar disc in hydrogen alpha with a Quark. This lets me use my longer scope and still get a full disc. Since narrowband doesn't care about achromatic glass, this reducer works perfectly since color isn't an issue. Sharp.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Oct 9, 2015Essential for full solar disk with my ASI 120MC camera.
Pros:Accurate,Lightweight,Strong Construction,Quality Lenses
Cons:Difficult To Focus
Comments:I use this for solar photography to get a full disk or half disk view on my sensor. In order to get to good focus you'll also probably need some spacer rings.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Jul 4, 2015Complements 2X nosepiece in binoviewer
Pros:Easy to Use,Sharp,Quality Lenses
Cons: Comments:I bought this 0.5X to partially restore field of view when using a 2X barlow nose piece in a binoviewer. I had to add about 2 inches of spacers between the two with the 2X closer to the objective, but I was able to get back to just above 1X (maybe 1.25X) magnification. The barlow alone yielded 3X with the additional BV path length, so this was a major improvement. The stars remain sharp across the field, but the introduced field curvature requires refocusing from about 50% out to the field stop, so not a perfect solution. That, and the obvious vignetting because so many outer rays are lost against the inner surface of the spacers by the diverging 2X unit. Tried reversing 2X-0.5X arrangement, but couldn't get anything remotely resembling a usable image. Also, the best arrangement is only useful for lowest powers. Above that, some coma becomes evident. Under those conditions, I just use the 2X unit alone for a perfect field edge to edge. Overall, a good deal, but budget for 1.25" spacers as well.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Jason Tang New Member
- Skill Level
- Unknown
- Time with Product
- Unknown
- User Notes:
- Review by Jason of NY, NY.
Jun 26, 2015When it works, it works well
Pros:Compact,Lightweight
Cons:Difficult to Use
Comments:The GSO Focal reducer works really well on applications that it was designed for - due to its aperture, it works better on eyepieces with a field stop of no greater then around 23MM. It can also be limited by the internal baffling if you have a SCT or a MAK.
Bottom Line: Would you recommend this item? Yes
However, it performs fantastically with my Mallincam, where it has found a permanent home.This review was provided courtesy of AgenaAstro.com
Jan 30, 2015GSO 1.25" 0.5x Focal Reducer by GSO
Pros:Compact,Easy to Use
Cons:Loose Fitting
Comments:Works well on Orion reflector and Meade Mak telescopes and does exactly what it is suppose to do. My only fear is that it screws on loosely to the camera but a little Teflon tape works great solving this fear.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Mar 30, 2014GSO 1.25" 0.5x Focal Reducer
Pros:Accurate,Lightweight,Quality Lenses,Easy to Use,Compact,Strong Construction
Cons: Comments:I was looking for something to give me a wider view on some nubulas and constellations. This works perfect and I can really recommend it to any-one with the same need. Great product and I like it very much.
Bottom Line: Would you recommend this item? NoThis review was provided courtesy of AgenaAstro.com
Dec 3, 2013Did the job.
Pros:Lightweight,Compact,Quality Lenses
Cons: Comments:I needed a wider image when using my DMK 21 camera and this focal reducer did the trick. I had to make my own adapter to mount the reducer directly to my camera and then it worked great.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Nov 30, 2013Using with ES 16mm and 20mm eyepieces
Pros:Easy to Use,Quality Lenses,Lightweight
Cons: Comments:I bought a pair of these to use with my 16mm and 20mm ES 68 eyepieces in my binoviewer. Attached each focal reducer to an eyepiece and this worked well. It didn't change the focus much with these eyepieces though I have another pair of 16mm UW80 eyepieces that I couldn't get to focus in my telescope when using them and the focal reducers in the binoviewer.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Mar 22, 2013Very useful Reducer
Pros:Easy to Use,Accurate,Lightweight,Strong Construction,Quality Lenses,Compact
Cons: Comments:I found it very useful, because of the high focal ratio of my scope, I was able to use my current eyepieces with this reducer to catch more of the sky.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Feb 26, 2012Good product, quick shipping
Pros:Lightweight,Compact,Strong Construction,Quality Lenses,Accurate,Easy to Use
Cons: Comments:Used to widen the field of view in medium focal length eyepieces
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Feb 24, 2012This may solve your problem
Pros:Quality Lenses,Strong Construction,Lightweight,Compact,Easy to Use
Cons: Comments:This is handy for either wide-field needs, or to make a CCD/photo exposure 4x more efficient. Turn your F10 SCT into an F5 SCT, etc.,.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Nov 5, 2011Excelent for its price
Pros:Accurate,Quality Lenses,Compact
Cons: Comments:It's a good product for its price. Quality is quite good. I don't see any difference by using it or a double mm eyepiece.
Bottom Line: Would you recommend this item? Yes
Worth its price.This review was provided courtesy of AgenaAstro.com
dbigers New Member
- Skill Level
- Unknown
- Time with Product
- Unknown
- User Notes:
- Review by Donnie of Western KY.
May 3, 2011Pretty good for visual also.
Pros:Compact
Cons:None
Comments:I bought this as an experiment. I recently bought a C90 Mak for use as a spotting scope. For use as a spotting scope I prefer to have a zoom. The popular 8-24mm zooms create 52x with the C90 at the lowest setting. That is a bit much for the low end. I bought this to attach to the zoom to see if I could get a better working range of powers. There is some vignetting at the lower end, but it is not terrible. Works well enough for my intended purpose and I am satisfied.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
May 23, 2010What a deal for the money!
Pros:Compact,Accurate,Strong Construction,Quality Lenses
Cons: Comments:Quite a bit of bang for the buck ..
Bottom Line: Would you recommend this item? Yes
Worked fine right out of the box .
Use this with my Stella Cam 3 on CGE 11
You wont cry if you loose this in the field, and maybe you will.
Only reason I did not give it 5 stars, is I am waiting for some kind of surprise from the product .
So far no surprise. Except it just works .This review was provided courtesy of AgenaAstro.com
Jan 18, 2010It performed as expected
Pros:Strong Construction,Only used one time so far,Quality Lenses,Compact,Accurate
Cons: Comments:Used reducer on Celestron CGE 1100 XLT SCT with NextImage web cam. I got the expected images I was looking for.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Jan 18, 2010Review GSO 1.25" 0.5x Focal Reducer
Pros:Accurate
Cons: Comments:I purchased the GSO 0.5x focal reducer for use with an auto-guider camera on an astronomical imaging equipment setup. It arrived quickly, was exactly as described in the sales literature, and works well.
Bottom Line: Would you recommend this item? Yes
All of this at a very good price.This review was provided courtesy of AgenaAstro.com
Nov 6, 2009Excellent thing!
Pros:Compact
Cons: Comments:I really like this focal reducer. My telescope has a long focal length and I need it often. It's very useful because it's small and has a good quality. Great thing!
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
May 26, 2009Great price!
Pros:Strong Construction,Compact,Accurate
Cons:Difficult To Focus
Comments:Had some problems getting to focus on my 6" Newtonian f/8 telescope with this reducer on my Orion SSDSCI, but it could be my fault, overall, it looks like a great buy for the price!
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
May 26, 2009Revelation
Pros:Compact,Accurate,Strong Construction,Quality Lenses
Cons: Comments:I was very dissapointed and frustrated by the fact that I could not find any guiding star with my guiding setup (Philips SPC900NC webcam and 70mm f10 refractor) in my light polluted area. A friend suggested the use of a 0.5x reducer. From the moment I first used it, I never looked back again. Finding a guiding star was child's play even in light polluted Athens!
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
May 10, 2009Great focal reducer
Pros:Comfortable Eyepiece,Accurate,Strong Construction,Quality Lenses
Cons: Comments:This focal reducer is great. I'm using it with my Phillips spc900nc webcam. I just screwed it to the adapter, meade etx-125 telescope, and I have gotten my best photos of Saturn using this.
Bottom Line: Would you recommend this item? Yes
This is a great piece to have and a great price!This review was provided courtesy of AgenaAstro.com
Mar 31, 2009Highly recommend the GSO 1.25 inch focal reducer
Pros:Quality Lenses
Cons: Comments:I highly recommend this lense. I have a ETX-125 and when in polar mode you just can't image anything near the NCP since there is little rooom when imaging through the rear of the scope. I successfully imaged M-51 and M-81 with great results. You can't beat the price either.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
AstroGuy1 New Member
- Skill Level
- Unknown
- Time with Product
- Unknown
- User Notes:
- Review by calastro of California.
Feb 2, 2009Very good performance!
Pros:Works well on cameras,Optics are excellent
Cons:None
Comments:I really wasn't expecting too much from this focal reducer because of the price. I was sure surprised!
Bottom Line: Would you recommend this item? Yes
While I haven't had the opportunity to fully put it through its paces, I am so far quite pleased with its results. I have used it with a variety of eyepieces from 12.5mm to 40mm. I have also used it with my LCL-902K CCD camera and have been quite impressed with the results.
I will say that for the price, if you use any kind of webcam, video, or CCD camera, this is a no brainer! It's a must have!This review was provided courtesy of AgenaAstro.com
Nov 18, 2008GSO 0.5x 1.25" Focal Reducer
Pros:Works perfectly with CCD,Works perfectly with EPs
Cons:No bad review
Comments:I received my new GSO 0.5X focal reducer last week and I have been testing this reducer on everything from my eyepieces to my imagers. It works great with the Orion Starshoot DSC and the Philips SPC 900NC webcam. I own an Orion 6" LT f/8 and with the very long focal ratio of the telescope, this 0.5x reducer is a must for imaging. Using the telescope listed above, this reducer has decreased the focal length from 1200mm to about 800mm, from what I can tell by using my Philips webcam, which has a FOV of a 52 degree 6mm plossl eyepiece without using the reducer, and now with the reducer installed the FOV is more like a 52 degree 12mm plossl eyepiece. This is also the same for using the Orion Starshoot DSC. What I like about using this GSO 0.5x focal reducer is that I haven't noticed any extra false color with my webcam or eyepiece. The edge of view is also not distorted.
Bottom Line: Would you recommend this item? YesThis review was provided courtesy of AgenaAstro.com
Apr 28, 2008Very good performance!
Pros:Optics are excellent! Works well on cameras!
Cons:None
Comments:I really wasn't expecting too much from this focal reducer because of the price. I was sure surprised!
Bottom Line: Would you recommend this item? Yes
While I haven't had the opportunity to fully put it throught its paces, I am so far quite pleased with its results. I have used it with a variety of eyepieces from 12.5mm to 40mm. I have also used it with my LCL-902K CCD camera and have been quite impressed with the results.
I will say that for the price, if you use any kind of webcam, video, or CCD camera, this is a no brainer! It's a must have!Jun 30, 2007GSO 0.5x 1.25" Focal Reducer
Pros:Great price and works perfectly with CCD imagers and eyepieces!!
Cons:No bad review!
Comments:I received my new GSO 0.5X focal reducer last week and I have been testing this reducer on everything from my eyepieces to my imagers.
Bottom Line: Would you recommend this item? Yes
Works great with the Orion Starshoot DSC and the Philips SPC 900NC webcam. I own an Orion 6" LT f/8 and with the very long focal ratio of the telescope, this 0.5x reducer is a must for imaging.
Using the telescope listed above, this reducer has decreased the focal length from 1200mm to about 800mm, from what I can tell by using my Philips webcam, which has a FOV of a 52 degree 6mm plossl eyepiece without using the reducer, and now with the reducer installed the FOV is more like a 52 degree 12mm plossl eyepiece. This is also the same for using the Orion Starshoot DSC.
What I like about using this GSO 0.5x focal reducer is that i haven't noticed any extra false color with my webcam or eyepiece. The edge of view is also not distorted.Sort bySpecifications
Manufacturer GSO
