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Star Watcher 72ED back focus problem

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53 replies to this topic

#51 Jaymz007

Jaymz007

    Lift Off

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  • Loc: Wisconsin

Posted 02 December 2021 - 07:15 PM

Well, I ordered the adapter (and a 10" dovetail plate) from First Light Optics. I have to give it up for those guys. Second order from them, both shipments arrived from across the pond in under a week!!
The adapter works like a dream. Now I have a fully threaded image train, like it should be.

Thanks again for the link!

 

Here are a couple of links to the pictures, to give perspective.

https://flic.kr/p/2mNhPqg

https://flic.kr/p/2mNrsWk


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#52 Shorty Barlow

Shorty Barlow

    Gemini

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  • Loc: Lloegyr

Posted 18 April 2025 - 09:01 PM

After many years of using the rev 1 version of this scope I've finally settled on three eyepieces used in conjunction with a TV 1.25" Everbrite.

 

3-8mm SvBony zoom

19mm TV Panoptic

 

1BPEmycl.jpg

 

Takahashi 32mm orthoscopic

 

Ix5rvpXl.jpg

 

Not only do I not have any back-focus issues, the overall balance is almost perfect. especially on the lightweight SW AZ5 tripod/mount.

 

bSrPRJtl.jpg

 

As a consequence this is my most used scope.



#53 Tropobob

Tropobob

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Posted 16 May 2025 - 02:24 AM

I just picked up a preowned one of these a few hours ago.  Let me first say, that I have too much equipment so I didn't need it, but its my hobby and U only live once. 

 

I have brought a mark one; it was for a reasonable price.  

 

Mucking around (Oh what fun!! (No sarcasm intended)), I believe that I have managed to get all eyepieces to focus, but not all in the one configuration. The best fit for me was extending the length of the focuser by using a cheap barlow (with the lens removed).    Oh, this was with a 1.25 inch diagonal.  I only have 2 x2 inch eyepieces and do no intended to those as I think it will upset the balance of the setup on my altz mounts. 

 

I thought the scope was already slightly, tail heavy (EP end), but my altz mount could handle that by tightening the clutches.  

 

I am fortunate too have so much equipment and thus options. This may have been difficult for others who are just starting out.



#54 PatrickVt

PatrickVt

    Apollo

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  • Loc: Vermont, US

Posted 16 May 2025 - 08:26 AM

I just picked up a preowned one of these a few hours ago.  Let me first say, that I have too much equipment so I didn't need it, but its my hobby and U only live once. 

 

I have brought a mark one; it was for a reasonable price.  

 

Mucking around (Oh what fun!! (No sarcasm intended)), I believe that I have managed to get all eyepieces to focus, but not all in the one configuration. The best fit for me was extending the length of the focuser by using a cheap barlow (with the lens removed).    Oh, this was with a 1.25 inch diagonal.  I only have 2 x2 inch eyepieces and do no intended to those as I think it will upset the balance of the setup on my altz mounts. 

 

I thought the scope was already slightly, tail heavy (EP end), but my altz mount could handle that by tightening the clutches.  

 

I am fortunate too have so much equipment and thus options. This may have been difficult for others who are just starting out.

 

I highlighted the phrase in bold above...   I also found that attaining equal balance to be impossible in certain circumstances in its stock configuration (especially if using my Quark and/or adding a camera) so I replaced that tiny green dovetail bar with a longer one and used a shorter one as a riser (see photo below) so that the longer dovetail bar extends under the focuser.  I didn't use the short lime green one as a riser for two reasons...  1)  I hate lime green...  2)  the two threaded holes in the short lime green dovetail bar were too close together for my liking.  

 

As far as coming to focus, it was only with a 2 inch diagonal that some 2 inch eyepieces wouldn't come to focus due to the tube being slightly too long and hence not enough available backfocus.  There are no problems with a 1.25 inch diagonal.  

 

Patrick

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