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Focus problems with GSO 6" f6 Newtonian

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#1 Skyfisher

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Posted 29 September 2022 - 08:40 PM

I am having problems with my Newtonian. It is a GSO 6" f6 OTA on a home made Dobsonian mount.  With a Celestron zoom eyepiece I can't quite focus because the Crayford focuser bottoms out before it is in focus.  A Teleview Plossl 25mm is barely (I think) in focus when the focuser bottoms out.   I assume that the primary needs to move towards the secondary?  Any suggestions appreciated.

 


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#2 vtornado

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Posted 29 September 2022 - 08:47 PM

Do you feel confident in re-collimating?

 

If so you can turn the collimation bolts all the way in, then back them out a bit to re-collimate.

That might get a few more millimeters.

 

I think a barlow will buy you some more space too.

 

========  PS =====

 

Other thoughts are is there an extension tube with the focuser?  Some of these modern scopes are setup

for photography and have an extension tube for eyepieces to reach focus.  You can try removing that if there is one.

but then you may have issues with not enough out focus.

 

If that is the case you can buy another extension shorter than the one that is in scope.

 

VT


Edited by vtornado, 29 September 2022 - 08:57 PM.

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#3 FRANKVSTAR

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Posted 29 September 2022 - 08:55 PM

Yes a good barlow will usually help with focus if your running out of travel. Then again I think they sell a shorty adapter for your eyepieces that will give you some extra room, its like an extender but very short,so the eyepiece set even closer to the bottom of the focuser. I have even had to take the barrel off the eyepiece and shorten it my self once or twice before,not pretty but it worked.


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#4 Skyfisher

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Posted 29 September 2022 - 09:02 PM

Do you feel confident in re-collimating?

 

If so you can turn the collimation bolts all the way in, then back them out a bit to re-collimate.

That might get a few more millimeters.

 

I think a barlow will buy you some more space too.

 

VT

VT,  I did collimate using a laser trying to get the mirror as close to the secondary as possible and plan to try again.  I am thinking of removing the mirror cell and seeing how I can gain a few more mm.  I can get maybe another mm by turning the 35mm extension tube down but not keen on that.   Buying a barlow isn't in the budget right now and doesn't really solve the issue.  Frustrated with this first scope frown.gif


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#5 Skyfisher

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Posted 29 September 2022 - 09:05 PM

Yes a good barlow will usually help with focus if your running out of travel. Then again I think they sell a shorty adapter for your eyepieces that will give you some extra room, its like an extender but very short,so the eyepiece set even closer to the bottom of the focuser. I have even had to take the barrel off the eyepiece and shorten it my self once or twice before,not pretty but it worked.

Thanks !  This is a 2" focuser with 35mm extension and 1.25" eyepiece adaptor.  I will look for another adaptor.  Suggestions for vendor of shorter adaptor ?



#6 Skyfisher

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Posted 29 September 2022 - 10:06 PM

I was able to remove the 35mm extension entirely and insert the 1.25" eyepiece adaptor part way and now can focus BUT it really isn't a good long term solution.   Maybe a short 1.25" extension ?



#7 Don H

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Posted 30 September 2022 - 03:31 PM

I was able to remove the 35mm extension entirely and insert the 1.25" eyepiece adaptor part way and now can focus BUT it really isn't a good long term solution.   Maybe a short 1.25" extension ?

The 35mm extension may simply be a bit too long for your visual application. This should be a fun scope to use and having it focus close to the middle of the focuser drawtube will enable you to use a wide variety of eps. You can search for an adapter that is shorter than 35mm for a very reasonable price. You might try one from this page. If you scroll down a bit, a .25 or .5 inch extension (about 6 or 12mm) might work well for you.

 

https://agenaastro.c...lt/?q=extension


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#8 Skyfisher

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Posted 30 September 2022 - 07:08 PM

The 35mm extension may simply be a bit too long for your visual application. This should be a fun scope to use and having it focus close to the middle of the focuser drawtube will enable you to use a wide variety of eps. You can search for an adapter that is shorter than 35mm for a very reasonable price. You might try one from this page. If you scroll down a bit, a .25 or .5 inch extension (about 6 or 12mm) might work well for you.

 

https://agenaastro.c...lt/?q=extension

I ordered this but not really what I was looking for. wanted a 2" X 10-25mm extension but can't find anything in that range.   I may end up making an extension from brass or aluminum if nothing suitable available.

 

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


Edited by Skyfisher, 30 September 2022 - 07:10 PM.


#9 Chad7531

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Posted 30 September 2022 - 07:16 PM

I ordered this but not really what I was looking for. wanted a 2" X 10-25mm extension but can't find anything in that range. I may end up making an extension from brass or aluminum if nothing suitable available.

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

Lumicon makes a 2” extension 1” long. I have one, but wouldn’t recommend it though. It’s cheaply made and annoying to use.

Edited by Chad7531, 30 September 2022 - 07:17 PM.

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#10 Skyfisher

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Posted 30 September 2022 - 09:30 PM

Lumicon makes a 2” extension 1” long. I have one, but wouldn’t recommend it though. It’s cheaply made and annoying to use.

Just looked at that.  You are correct.  Amazing to be so shoddy w/o the brass ring inside.




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