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SkyWatcher 127 + GSO 2" focuser

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#1 Conaxian

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Posted 28 March 2019 - 09:07 PM

Hello gang. I have been tampering with my mak again, and I learned something that might save someone $25 in the process.

Since my mount is sloppy in azimuth and wobbles when I try to focus high power eyepieces, while the elevation axis is rock solid, I decided to attempt a mod on the focuser.  I got a GSO 2-speed 2" and an SCT adapter ring for maks from Agena.  It turns out the adapter is unnecessary, the rear fitting works fine with an SCT focuser.  I guess I will return the ring. Any SCT visual back or accessory will work with these scopes.

Before you order this focuser you need to know that it will interfere with the OEM focus knob.  It's large and interferes with the mirror moving knob.

I got around this by removing the stem to test fit the ring, marked the position of the knob, removed the ring and relieved the problem with a dremel and grinder wheel. The focuser's gnurled ring is soft aluminum and the job only took a minute. About 2mm is ground away in an area about 1/2" long.

The ring's 'damaged' spot is hidden by the focuser knob anyway, you can't see the butchery.

Now I won't have to deal with image shift or my sloppy azimuth axis. It should be nice for getting the sharpest views as well. I am going to adjust the mirror's focus to optimum, then check and adjust the collimation with the new gear installed.

The mirror's focus knob rubber cover acts like a brake, it should keep the focus from moving around, yet it can still be turned if needed. It is against the focuser ring enough to have some friction.

 

The forum here has given me many tips and I felt the need to give one back.

Enjoy your new planet killers! wink.gif


Edited by Conaxian, 28 March 2019 - 09:07 PM.


#2 Peter Besenbruch

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Posted 28 March 2019 - 09:56 PM

Cool. You must have one of the newer 5" models, since you didn't need an adapter. I use the same focuser on my 7".


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#3 Conaxian

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Posted 28 March 2019 - 10:14 PM

Cool. You must have one of the newer 5" models, since you didn't need an adapter. I use the same focuser on my 7".

Yup, bought new in October '18, It came with the 2" diagonal and EP.

Too bad I bought the adapter, I was sure it would need it.

Did you need the adapter for your 180?


Edited by Conaxian, 28 March 2019 - 10:18 PM.


#4 Peter Besenbruch

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Posted 29 March 2019 - 06:34 PM

Did you need the adapter for your 180?

No, the 180 was redesigned a while back (2014 or 15?). It was a fairly thorough redesign, combining a larger primary mirror, and a larger primary baffle opening to go with the 2" visual back. I'm not sure what Synta did with the 127mm besides making it SCT accessory friendly.


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#5 Cali

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Posted 31 March 2019 - 01:04 PM

Yup, bought new in October '18, It came with the 2" diagonal and EP.

Too bad I bought the adapter, I was sure it would need it.

Did you need the adapter for your 180?

Can you send a link to the GSO 2-speed 2" ? Not sure if I'm looking at the right piece of equipment.

 

Thx

 

- Cal


Edited by Cali, 31 March 2019 - 01:05 PM.


#6 Conaxian

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Posted 01 April 2019 - 02:14 AM

Can you send a link to the GSO 2-speed 2" ? Not sure if I'm looking at the right piece of equipment.

 

Thx

 

- Cal

Certainly-

https://agenaastro.c...-telescope.html

 

This is the one I put on. For storage of the tube the focuser can be quickly removed by loosening the rotation locking thumbscrew on top, leaving just the mounting ring on the tube.  This leaves the scope shorter than when it had the SkyWatcher VB on it. Nice for small cases. (That visual back will also fit SCT's.)

Regards!


Edited by Conaxian, 01 April 2019 - 02:29 AM.

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#7 Conaxian

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Posted 01 April 2019 - 02:25 AM

Anyone planning to do this- when you loosen and remove the focus knob's black collar shaft (with the two set screws) you need to have the scope tipped upward or the primary and its baffle can come loose and move forward. That collar shaft (or whatever it is called) holds it in place. The collimation screws are not securing the mirror/focuser bracket assembly.

Careful  wink.gif


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#8 Luckypaul777

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Posted 25 April 2019 - 11:25 AM

Does anyone know if OPT's house brand TPO focuser is the same as the Agena Astro GSO focuser? Bought one for a Skywatcher 127 mak but looks like it is too big, not sure I want to attempt working on the stock focuser. If I have the wrong external focuser. Thanks.

 

Paul 



#9 Conaxian

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Posted 25 April 2019 - 05:21 PM

Does anyone know if OPT's house brand TPO focuser is the same as the Agena Astro GSO focuser? Bought one for a Skywatcher 127 mak but looks like it is too big, not sure I want to attempt working on the stock focuser. If I have the wrong external focuser. Thanks.

 

Paul 

Hi Paul, I just looked up the OPT focuser. The dual speed is priced the same as the GSO, the pictures didn't show if it had graduations etched in the tube, the GSO one does.  Anyway, if it is the same, it is too big for the 127 mak.  That is why I wrote this up above:

 

"Before you order this focuser you need to know that it will interfere with the OEM focus knob.  It's large and interferes with the mirror moving knob.

I got around this by removing the stem to test fit the ring, marked the position of the knob, removed the ring and relieved the problem with a dremel and grinder wheel. The focuser's gnurled ring is soft aluminum and the job only took a minute. About 2mm is ground away in an area about 1/2" long.

The ring's 'damaged' spot is hidden by the focuser knob anyway, you can't see the butchery."

 

The primary mirror is free to move forward when you push the focuser shaft inward, so it is a delicate operation.  If you don't want to undo the meniscus cell and  focusing mechanism, you won't be able to install the SCT focuser.  Some guys are more comfortable tinkering with scopes than others. If you decide to send it back, don't feel bad I almost sent mine back and for the same reason.  It is stressful taking apart a perfectly good optic for minor improvements. Maybe a GSO 1 1/4" focuser would work without mods.

 

You have to remove the rubber knob cover, remove the locking sleeve (2 set screws), press the shaft inward to get clearance, thread the new focuser ring into place, mark the ring where the focuser shaft interferes, remove and relieve the ring with a file or dremel, thread it back on and then finagle the original shaft back into place. Having the meniscus off is probably necessary. The primary and focus plate goes back into place with a clunk. I used the outer primary baffle tube (the part attached to the primary) as a handle.

After that the new focuser can be removed by loosening the rotation lock screw and popping it off. Watch out for the black oily grease in there, it's nasty.

 

The good part is that focusing is now precise and easy with no mirror movement at all.  You also get a slightly longer F/L.

Cheers!



#10 Luckypaul777

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Posted 26 April 2019 - 10:18 AM

Conaxian,

Thanks for the detailed reply, I can see it is not something I would attempt for fear of making the scope unusable. I put a Twilight on a 9.25 and it screwed right on, as well as one a 8" SCT. Should have read your post before I bought it but planning on getting an SW 180 it should fit on it.

 

Paul 


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#11 Conaxian

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Posted 26 April 2019 - 11:54 AM

I don't blame anyone for being careful about their telescope. These things don't grow on trees.  I'm glad you will have another use for it.

I hate doing returns myself. I only returned that adapter because I have absolutely no use now or ever for it.




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