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Skywatcher Dobsonian focuser issue!

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11 replies to this topic

#1 BlueTrane2028

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Posted 28 September 2020 - 10:43 PM

Sooo... I went on a "quality eyepiece" binge recently.  I put that in quotes because I don't have TeleVue money, but banishing almost everything that's under 82 degrees is IMO a good step toward "quality."

Since I now have a few 2" eyepieces, when I saw a 2" 2x Barlow at a local shop for what I considered to be a decent price, I jumped on it.

It's an Orion apochromatic 2x, originally sold for something like $190, I snagged it for $50.  Super stoked.

So, I say to myself, "let's barlow the 20mm UWA and see how it looks on planets."

I mount everything in the focuser and look up... and find that there's not enough in travel to focus the eyepiece.

Upon further review, those who don't know, Skywatcher's focusers have extension pieces that are necessary to be present to achieve focus, the scopes come with one for 1.25" and one for 2".

That extension has a ridge inside it that's preventing my barlow from going deep enough into the focuser.  If I were to mill out the ridge, the eyecrometer says that it would ruin the extension, preventing it from being able to be mounted in the first place.

Has anyone heard of a longer focuser tube instead of needing adapters?  Without using the extension, then there isn't enough OUT travel on the focuser, and the screws mar the finish of the barlow.... sadly I tried it, didn't realize what was happening until I was around some light.  It's not super bad and the function isn't hindered, but the thing was in likely never before removed from the box condition.  Such is life.

So, I'm at the point of, is there a focuser option, do I set the thing aside for a future refractor, or do I get an entirely different reflector to be able to use thing?


Edited by BlueTrane2028, 28 September 2020 - 10:52 PM.


#2 Tfer

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Posted 28 September 2020 - 11:30 PM

Get your hands on the cheapest 2” Barlow you can find.

 

Unscrew, and remove the lens.  Instant focal extender. 



#3 Ihtegla Sar

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Posted 28 September 2020 - 11:57 PM

Maybe a higher quality extender? I replaced the extender on my Skywatcher with something a little more robust, like this:


https://www.amazon.c...LWDX?th=1&psc=1

The 35mm extender is a little shorter than the stock extender but it's long enough to breach focus with all my eyepieces so it might work for your Barlow.

But then I got an HRCC coma corrector from Explore Scientific and it works in my Skywatcher without needing an extension (the HRCC needs a lot of infocus). So now I just use the HRCC most of the time and the extension spends most of its time in the parts box.

Edited by Ihtegla Sar, 29 September 2020 - 12:05 AM.

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#4 SteveG

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Posted 29 September 2020 - 07:00 PM

Get your hands on the cheapest 2” Barlow you can find.

 

Unscrew, and remove the lens.  Instant focal extender. 

That would be an extension tube. You can buy them without optics:

https://www.amazon.c...r/dp/B01NBILIO2

 

My suggestion, buy a 1.25” barlow instead. It will likely focus without an extension tube, and will be less weight and bulk hanging off the focuser.



#5 Eddgie

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Posted 30 September 2020 - 07:58 AM

Sooo... I went on a "quality eyepiece" binge recently.  I put that in quotes because I don't have TeleVue money, but banishing almost everything that's under 82 degrees is IMO a good step toward "quality."

Since I now have a few 2" eyepieces, when I saw a 2" 2x Barlow at a local shop for what I considered to be a decent price, I jumped on it.

It's an Orion apochromatic 2x, originally sold for something like $190, I snagged it for $50.  Super stoked.

So, I say to myself, "let's barlow the 20mm UWA and see how it looks on planets."

I mount everything in the focuser and look up... and find that there's not enough in travel to focus the eyepiece.

Upon further review, those who don't know, Skywatcher's focusers have extension pieces that are necessary to be present to achieve focus, the scopes come with one for 1.25" and one for 2".

That extension has a ridge inside it that's preventing my barlow from going deep enough into the focuser.  If I were to mill out the ridge, the eyecrometer says that it would ruin the extension, preventing it from being able to be mounted in the first place.

Has anyone heard of a longer focuser tube instead of needing adapters?  Without using the extension, then there isn't enough OUT travel on the focuser, and the screws mar the finish of the barlow.... sadly I tried it, didn't realize what was happening until I was around some light.  It's not super bad and the function isn't hindered, but the thing was in likely never before removed from the box condition.  Such is life.

So, I'm at the point of, is there a focuser option, do I set the thing aside for a future refractor, or do I get an entirely different reflector to be able to use thing?

I am confused by your post, but if I understand it correctly and the problem is that you cannot reach focus with the extension tube because don't have enough inward focuser travel, the remove the extension tube!

 

This will greatly shorten the focuser tube.  If the Barlow is a 1.25" Barlow, you would next simply use a 2" to 1.25" adapter.  This will reduce your focuser tube effective length by about 20mm.

 

https://optcorp.com/...lhoCvQkQAvD_BwE

 

If the only thing you need the adapter for is the Barlow, just leave it on the Barlow.

 

No one sells longer tubes for your focuser but the issue with a longer tube is that it would stick down into the light path too much when you were running without the extension.

 

If you buy an Moonlight focuser, you can get tubes up to 2.7" (or something like that) and by careful tuning you can set the focuser to a height that should work well for many different kinds of optics like Barlow and light binoviewers. 


Edited by Eddgie, 30 September 2020 - 07:59 AM.


#6 Eddgie

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Posted 30 September 2020 - 10:50 AM

I missed that the new Barlow was 2" but this makes even less sense unless your scope is different than any I have owned.

 

I guess the reason I thought you were using a 1.25" is because otherwise, you could have just removed the extension and used the Barlow directly in the focuser. 

 

I do this all the time.  I use the binoviewer without the extension and I use my filter wheel and focal reducer without the extension.

 

XQE_01141.JPG

 

Anyway, sorry for my confusion. I guess I just don't understand the problem and I was only trying to help.
 

 



#7 aeajr

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Posted 30 September 2020 - 10:56 AM

Have you tried the barlow without the extension tube?

 

I have an Apertura AD12 that came with an extension tube.  I never use it.  

 

Your scope may require it for some eyepiecs but not others.  Try it without.



#8 Ihtegla Sar

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Posted 30 September 2020 - 01:36 PM

We haven't heard back from the OP but he said "Without using the extension, then there isn't enough OUT travel on the focuser, and the screws mar the finish of the barlow...." So it sounds like using the Barlow without an extension tube won't work.

My suggestion was a shorter (35m) and better built extension tube than the original SW extension tube . . .
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#9 Old Rookie

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Posted 30 September 2020 - 03:00 PM

The OP can temperarily replace the original 2" adapter with a 35mm extension tube.  They can be had for $20 - $35.  I have and have used an Apertura extension tube on my 10" Flextube with good results.  There is a difference of 12mm between the two that would allow for inward travel when using the barlow.  The original Skywatcher 2" adapter has a length of 46mm and the Apertura 35mm extension tube has a length of 34mm.  This is just one option, I'm sure there are others.

Attached Thumbnails

  • Original_Adapter.jpg
  • 35mm_Extension.jpg


#10 Ihtegla Sar

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Posted 30 September 2020 - 03:39 PM

The OP can temperarily replace the original 2" adapter with a 35mm extension tube. They can be had for $20 - $35. I have and have used an Apertura extension tube on my 10" Flextube with good results. There is a difference of 12mm between the two that would allow for inward travel when using the barlow. The original Skywatcher 2" adapter has a length of 46mm and the Apertura 35mm extension tube has a length of 34mm. This is just one option, I'm sure there are others.


Nice photos! That's just what I was thinking, but a picture is worth 1000 words.

#11 BlueTrane2028

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Posted 01 October 2020 - 11:26 PM

The OP can temperarily replace the original 2" adapter with a 35mm extension tube.  They can be had for $20 - $35.  I have and have used an Apertura extension tube on my 10" Flextube with good results.  There is a difference of 12mm between the two that would allow for inward travel when using the barlow.  The original Skywatcher 2" adapter has a length of 46mm and the Apertura 35mm extension tube has a length of 34mm.  This is just one option, I'm sure there are others.

Does a long 2" barlow fully insert into the focuser with this pictured tube? Mine is bottoming out in the one that comes with the scope.



#12 Old Rookie

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Posted 02 October 2020 - 07:27 AM

Does a long 2" barlow fully insert into the focuser with this pictured tube? Mine is bottoming out in the one that comes with the scope.

Not with this particular Apertura/GSO extension tube.  It has an inside ridge at about the 34mm mark.




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