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For Orion 120ST, which GSO 2'' Crayford Focuser dual speed to purchase, 96mm or 112mm

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#1 stanylee

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Posted 20 October 2019 - 11:47 PM

I'm a newbie. In the compatibility chart for GSO 2'' dual speed crayford focuser, it says either 96mm or 112mm model is compatible with Orion AstroView 120st. It seems 96mm is to install onto the collar, while the 112mm one is to install inside the tube directly. I wonder which one would be suggested and easier to install and use. I will probably also just remove the stock focuser and measure the tube myself. Thanks.

 

https://agenaastro.c...patibility.html


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#2 msl615

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Posted 21 October 2019 - 01:03 AM

It looks like either is OK from their table. Either the 96 bolts into the collar already there, or the 112 bolts straight into the tube. How easy is it to remove the collar? If no problem, then maybe the 96 because it is slightly less $$?

 

 

Mike



#3 wrvond

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Posted 21 October 2019 - 05:44 AM

Either will work just fine. As Jon Isaacs pointed out to me, if you decide to move to another scope, the 112 mm will only fit 120mm OTAs but the 96mm will fit pretty much any tube using an adapter ring.

 

I installed the 112mm onto a Meade R5; it was a very tight fit, I had to sand the inside of the OTA to get it to go in. Now that I've moved on to a SW 120 I can't get the GSO focuser out of the Meade in order to put the OEM focuser back in and sell the scope. Not a real problem, but if I were to try to sell a focuser without an OTA I'd have better luck selling the GSO than the Meade.


Edited by wrvond, 21 October 2019 - 05:48 AM.


#4 SloMoe

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Posted 21 October 2019 - 06:59 AM

Personally, very small market for the original focuser anyway as that most are looking to do the same upgrade you did, and as for resale like anything in this hobby an upgrade will slightly increase the scopes value but you'll never sell if for what you have invested in it.

 

The ring adds weight, not much and it add's the possibility of sight alignment error, I got a GSO direct fit for my Orion ST-90, put the original focuser in the classifieds, still have it, makes an interesting candle holder. 

 

First thing I did when I received the GSO was take it apart to clean & lube everything that moves and secured all the screws quality control missed.

 

BTW, love the GSO focuser.


Edited by Mike W., 21 October 2019 - 07:11 AM.


#5 MalVeauX

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Posted 21 October 2019 - 09:23 AM



I'm a newbie. In the compatibility chart for GSO 2'' dual speed crayford focuser, it says either 96mm or 112mm model is compatible with Orion AstroView 120st. It seems 96mm is to install onto the collar, while the 112mm one is to install inside the tube directly. I wonder which one would be suggested and easier to install and use. I will probably also just remove the stock focuser and measure the tube myself. Thanks.

 

https://agenaastro.c...patibility.html

Heya,

 

Depends on which one you want. The 112mm is the one that directly inserts and fits. The 96mm would need a new flange. Also it depends if you're talking about the standard crayford or the linear bearing. The linear bearing you only one have option, the 112mm, because it doesn't take an addition flange at all (only the smaller models can have a flange swap out). Very few scopes use 112mm, the 96mm is common. So depends if you think you might want to re-use the focuser on another scope, or re-sale it later, etc. Personally I put a 112mm into mine. I buy these focusers used when possible and I tend to go for the linear bearing where possible to get the extra weight tolerance because I image, but also use heavy trains with binoviewers, big 2" eyepieces, Quark, etc.

 

ST120 + GSO Linear Bearing 112mm

 

48530070152_5651874d3e_c.jpg

 

ST120 + GSO Linear Bearing 112mm + Quark + Binos

 

48606945678_c632537687_c.jpg

 

Note, there have been reports that the tolerance of the latest versions of the GSO 112mm and the ST120 is off a little bit for some people and they're unable to install the focuser without shaving some metal. Keep this in mind.

 

Very best,


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#6 BYD

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Posted 21 October 2019 - 09:32 AM

Just bought one for my ST120, working flawlessly:

https://www.telescop...ser/p/13032.uts

 

You may find posts claiming that there's some issue with GSO one.


Edited by BYD, 21 October 2019 - 03:19 PM.


#7 stanylee

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Posted 21 October 2019 - 01:04 PM

Thank you all for the inputs. My 120ST looks to have a collar to me. I unscrewed the stock focuser and measured the inside diameter of the collar, and it is indeed around 96mm.



#8 tony_spina

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Posted 21 October 2019 - 05:36 PM

Get the 96mm.. that is what I use



#9 wrvond

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Posted 21 October 2019 - 08:01 PM

Thank you all for the inputs. My 120ST looks to have a collar to me. I unscrewed the stock focuser and measured the inside diameter of the collar, and it is indeed around 96mm.

Don't forget to order an extension tube.



#10 Binojunky

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Posted 22 October 2019 - 09:57 AM

I put the 96 on my ST120, three screws out, three in, time 5 minutes also fitted the optional finder shoe, and yes as pointed out a tube extension may be needed,Dave.


Edited by Binojunky, 22 October 2019 - 09:58 AM.

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#11 tony_spina

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Posted 22 October 2019 - 05:05 PM

I put the 96 on my ST120, three screws out, three in, time 5 minutes also fitted the optional finder shoe, and yes as pointed out a tube extension may be needed,Dave.

I have yet to find an eyepiece that needs a tube extension with the 96 focuser


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#12 Binojunky

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Posted 23 October 2019 - 10:24 AM

I have yet to find an eyepiece that needs a tube extension with the 96 focuser

Good point, in fact even though I have one I cannot remember using it D.



#13 stanylee

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Posted 08 November 2019 - 03:11 PM

I purchased the 96mm one. It fits perfectly, and I don't need an extension tube to focus with either 3.2mm or 25mm eyepieces. However, I don't see any mounting place for my finder scope, but the stock focuser has one.

How do you usually mount the finder scope on the combination of orion 120st and gso dual speed focuser?

#14 outofsight

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Posted 08 November 2019 - 03:25 PM

https://agenaastro.c...rd-focuser.html

 

That should point you in the right direction, pun not really intended.


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#15 stanylee

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Posted 09 November 2019 - 11:46 AM

Thanks for the pointer.
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#16 LDW47

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Posted 29 November 2019 - 09:11 PM

I purchased the 96mm one. It fits perfectly, and I don't need an extension tube to focus with either 3.2mm or 25mm eyepieces. However, I don't see any mounting place for my finder scope, but the stock focuser has one.

How do you usually mount the finder scope on the combination of orion 120st and gso dual speed focuser?

With a 2”, low power, wide field ep why would anyone need a finder ? The scope is the finder !


Edited by LDW47, 29 November 2019 - 09:12 PM.


#17 Don Allen

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Posted 04 December 2019 - 09:14 AM

What are the view like with this scope like when you sweep the sky at 40 or 50 mag?  How is the summer Milky Way?  The Double Cluster, etc..



#18 John Fitzgerald

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Posted 04 December 2019 - 09:21 AM

What are the view like with this scope like when you sweep the sky at 40 or 50 mag?  How is the summer Milky Way?  The Double Cluster, etc..

I put an old Moonlite on mine, the model built for a Synta that cannot be interchanged with adapters.   Works great.  No extension needed.  This scope gives outstanding views of the  milky way and open clusters using the 12mm ES 92 at 50x.



#19 wrvond

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Posted 04 December 2019 - 09:57 AM

I purchased the 96mm one. It fits perfectly, and I don't need an extension tube to focus with either 3.2mm or 25mm eyepieces. However, I don't see any mounting place for my finder scope, but the stock focuser has one.

How do you usually mount the finder scope on the combination of orion 120st and gso dual speed focuser?

The easiest way is to purchase a Synta style dovetail mount, drill a hole (or two) in the OTA, and screw it down.

 

IMG 1809


#20 SteveG

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Posted 04 December 2019 - 05:58 PM

Just bought one for my ST120, working flawlessly:

https://www.telescop...ser/p/13032.uts

 

You may find posts claiming that there's some issue with GSO one.

How long is the focus travel on this Orion focuser?



#21 SloMoe

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Posted 05 December 2019 - 08:04 AM

After I put the GSO on my 90 I did the finder shoe on the side like they show in the linked article, works great, and you can purchase a shoe that's got slots in it for this application too. 

https://agenaastro.c...nder-xfurb.html

 

But using a red dot that far back is a neck strain so I also mounted a shoe on my dew shield forward, 

My dew shield is threaded so I rotate it where I want it when slewing around on a GEM.

 

Lot like this photo, but this is a Mak but you get the idea.

Attached Thumbnails

  • thumbnail_processed.jpg

Edited by SloMoe, 05 December 2019 - 09:41 PM.


#22 Shorty Barlow

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Posted 05 December 2019 - 08:33 AM

The GSO96 is very well made and the focusing mechanism is smooth.

 

med_gallery_249298_10284_182834.jpg

 

However, the rotational mechanism can produce issues in my experience. GSO actually admit that it is weak feature and recommend that it shouldn't be utilised regularly. If you don't rotate the focuser very often it's fine. If you plan on rotating it a lot it might be wiser to buy the Sky-Watcher equivalent.

 

gallery_249298_10284_38130.jpg



#23 SloMoe

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Posted 05 December 2019 - 09:44 PM

With a 2”, low power, wide field ep why would anyone need a finder ? The scope is the finder !

Only when you're using low mag eyepieces, it's for when you kick up the mag the fov decreases dramatically over 125X, like for planetary even sometimes lunar viewing.


Edited by SloMoe, 05 December 2019 - 09:50 PM.


#24 JOEinCO

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Posted 06 December 2019 - 08:28 AM

.......However, the rotational mechanism can produce issues in my experience. GSO actually admit that it is weak feature and recommend that it shouldn't be utilised regularly. If you don't rotate the focuser very often it's fine. If you plan on rotating it a lot it might be wiser to buy the Sky-Watcher equivalent.

Actually, the rotational mechanism on any of these Chinese focusers, from the GSO to the Orion and even Explore Scientific's refractor focusers, can be DRAMATICALLY IMPROVED by simply replacing the three set screws of the rotating mechanism with nylon set screws.

 

Full nylon set screws let you adjust the tension tighter than the stock metal/nylon-tipped metal set screws, yet the focuser will rotate smoother than with the stock screws. And the full nylon set screws will never gouge the flange that the set screws ride in. It is a simple upgrade that makes for a huge improvement. 

 

Try a true hobby shop - on that caters to the radio control airplane crowd. If you can't find full nylon set screws locally, you can use the more-common nylon bolts (hex head or Allens) if you don't mind the head sticking out of the focuser slightly. Scope Stuff might have them, too. Buy 'em long; you can easily cut them to length with a razor blade.


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#25 SloMoe

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Posted 06 December 2019 - 08:41 AM

nylon set screws, never thought of that one, good excuse to visit the RC shop   smile.gif




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