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Opinions about GSO 200mm f/5?

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#1 fschuindt

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Posted 22 November 2020 - 06:59 AM

Hello there, everyone.

 

Recently I saw the opportunity of acquiring a GSO 200mm (7.87") f/5 OTA.

 

Here is a illustrative picture:

newton-200mm-f5-1000-500x416.jpg

And here's the only URL about it that I found: https://tellescopio....co-gso-200mm-f5

 

I was unable to find reviews on it so I decided to ask here if someone owns one of these or what are your impressions about GSO in general, or if you own other products or just have any idea/comment to share. I got interested into this OTA but I know very little about GSO.

 

Any comment is welcome, thank you.

 



#2 macdonjh

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Posted 22 November 2020 - 10:08 AM

I own a GSO 8" f/5.  I bought it used in March or April.  I enjoy using it.  The mirrors in mine are fine, though I'm not what you'd call a critical observer.  The vast majority of the time, I casually observe the moon, planets and sometimes double stars from my driveway.  The GSO has been fine for that.  I am also looking forward to using it in the week or so leading up to Jupiter's and Saturn's conjunction in December.  That's really why I bought it: wider field for things like that.

 

The GSO two speed focuser is pretty good.  I have Feather Touch and MoonLite focusers on my other scopes, but the GSO holds its own.  The rear cell doesn't hold collimation that well, but it's entirely possible I lose collimation because I store my scope standing up on its rear cell.

 

It's pretty heavy for an 8" scope.  I have added a third ring, though, for a Wilcox Ring set-up, since I use my scope on an equatorial mount.  I need to put it on a scale, but I think it's quite a bit heavier than my 8" classical Cassegrain.

 

As you can see, I've done some work on my scope.  It was a project during the early days of covid.  I was bored.

 

13 Finished.JPG

 

14 Rear.JPG

 

You can't see it in these photos, but I also used Protostar flock board to darken the entire inside of the OTA.  That's likely overkill, some people flock the area around the focuser (and sometimes only directly "behind" the secondary mirror) as well as a few inches in front of the primary mirror.  There was so little difference in cost (with shipping), I just flocked the whole OTA.


Edited by macdonjh, 22 November 2020 - 10:09 AM.

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#3 stargazer193857

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Posted 22 November 2020 - 11:35 AM

I own a GSO? 8" f4.9 OTA. The Foucault image looked much smoother than I expected, though I'm not sure if it is GSO. I bought it on Craigslist with scratches on the tube.

I like this size as a minidob because it fits in a small trunk complete without needing disassembly. Also not too short for a low stool or chair.
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#4 fschuindt

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Posted 22 November 2020 - 02:34 PM

Thank you for the insights macdonjh and stargazer193857. But I'll pass this time, nothing related to GSO, I think it's a good brand. But thinking more trough it I have a 210mm f/6.62 laying here, would be better for me to put it to use instead of buying another scope, I think that's what I'll do.


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#5 stargazer193857

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Posted 22 November 2020 - 02:52 PM

Thank you for the insights macdonjh and stargazer193857. But I'll pass this time, nothing related to GSO, I think it's a good brand. But thinking more trough it I have a 210mm f/6.62 laying here, would be better for me to put it to use instead of buying another scope, I think that's what I'll do.


If you already have an 8", I agree. The 6.62" has more native magnification and also sharper edge stars without a coma corrector. I just won't fit in some trunks, and needs a chair higher than a camping chair.

#6 Echolight

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Posted 22 November 2020 - 11:16 PM

The GSO f5 is likely optimized for AP with an oversized secondary and the need for a focuser extension.


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#7 macdonjh

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Posted 23 November 2020 - 04:33 PM

Echolight, I believe you are correct. It still makes a fine scope for quick weeknight visual. If I want more magnification and less central obstruction I use my classical Cassegrain.
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#8 doug mc

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Posted 23 November 2020 - 06:30 PM

I just bought one of these, and it is a fine scope. The secondary minor axis is 62mm (close to 30%). Smaller than your average SC and a GSO CC. I had to change the mirror cell springs as the original ones were not doing the job. Collimation is now a snap. Star test shows no astigmatism, but may have slight under correction. Stars in focus show clean diffraction patterns. The Luna terminator the other night with my binos was a jaw dropper. The fact that a 35mm eyepiece extension is required to reach focus with eyepiece is a bonus. It allows ease of reaching focus with binoviewers and an OCS. I can even reach focus with the 1.6x William Optics OCS in my binos. I am well and truly over being overly concerned about a slightly larger secondary than optimal. It's a keeper.

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Edited by doug mc, 23 November 2020 - 06:41 PM.

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#9 Helder

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Posted 25 November 2020 - 09:43 AM

has anyone managed to adapt an electronic focuser on the OTA 200mm from GSO?

#10 Echolight

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Posted 25 November 2020 - 11:42 AM

I just bought one of these, and it is a fine scope. The secondary minor axis is 62mm (close to 30%). Smaller than your average SC and a GSO CC. I had to change the mirror cell springs as the original ones were not doing the job. Collimation is now a snap. Star test shows no astigmatism, but may have slight under correction. Stars in focus show clean diffraction patterns. The Luna terminator the other night with my binos was a jaw dropper. The fact that a 35mm eyepiece extension is required to reach focus with eyepiece is a bonus. It allows ease of reaching focus with binoviewers and an OCS. I can even reach focus with the 1.6x William Optics OCS in my binos. I am well and truly over being overly concerned about a slightly larger secondary than optimal. It's a keeper.

Looks like a nice setup. I considered dob mounting one on a short tripod as a small richfield widefield scanning scope with a 3+ degree TFOV.



#11 doug mc

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Posted 25 November 2020 - 06:08 PM

Looks like a nice setup. I considered dob mounting one on a short tripod as a small richfield widefield scanning scope with a 3+ degree TFOV.

I managed to find some aluminium tubing the same diameter as the original stainless (1.75 inch). Cut them shorter than original and fitted them. Any movement now is mostly coming from the weak rings.



#12 doug mc

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Posted 26 November 2020 - 06:54 PM

Out again last night with my new 8 inch f/5 GSO. Had the fan running before viewing. The star test this time showed near identical extra focal star patterns, better this time than last.  Cooling a bit longer makes a difference. I have a ronchi test strip. Could not detect any differences either side of focus. Nice straight lines.




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