Wobbly star diagonal

[Andy R]

Hello,

 

right looked out out the window tonight and noticed it was clear sky’s whoop whoop, grabbed my scope and its currently cooling down outside. Started getting the rest ready gave EP a quick clean, got my diagonal out (it’s a star-watcher 1.25 Di-electric) and I noticed the shaft that the EP fixes into is wobbly. I haven’t noticed this before it’s only the 3rd time I’m going to use it. Has anyone any knowledge of these diagonals, and if so can I open the back and tighten it I’ve tried winding it clockwise but it doesn’t tighten so I’m thinking maybe there is a compression fitting inside?  Anyhow I’m off out to see if the view is affected 

thanks all. 

[Louis D]

Diagonal barrels generally screw into the diagonal housing.  If it is spinning freely and wobbling, it sounds like the threads have been stripped.  If that is the case, I wouldn't use it.  Try backing the barrel out by turning it counter-clockwise while applying slight pulling pressure to hopefully re-engage the threads and back it out to figure out what is damaged.  It may take some trial and error to get the threads realigned to be able to back it out.  This won't fix anything, but at least you'll know what's damaged.

[mikeDnight]

It might simply be that the barrel needs tightening by turning it clockwise. 

[Astro Imp]

9 hours ago, Andy R said:

gave EP a quick clean,

Why? With the small use your EP has had this shouldn't be necessary. 
If you must clean your optics take great care, you don't want to scratch the surface or damage the coatings.

[happy-kat]

Ditto above, they shouldn't need cleaning and even if dusty it doesn't effect the view.

[Louis D]

7 hours ago, mikeDnight said:

It might simply be that the barrel needs tightening by turning it clockwise. 

 

14 hours ago, Andy R said:

I’ve tried winding it clockwise but it doesn’t tighten

I assumed in my response the OP had already attempted that without success as it was my first thought.  If the housing is plastic rather than metal, it could have stripped quite easily.

[Andy R]

1 hour ago, Louis D said:

the housing is plastic rather than metal, it could have stripped quite easily.

Hi yep it’s prob stripped thread, I’m seeing a wee bit of fine swarf on the mirror that wasn’t there before. I’m thinking of asking if I can send it back or I may just glue it in place thanks anyhow. 

 

7 hours ago, Astro Imp said:

Why? With the small use your EP has had this shouldn't be necessary. 

How do you know how much use my EP has had  

I asked for advice on my star diagonal not for my lens cleaning to be scrutinised ?

[Waldemar]

39 minutes ago, Andy R said:

How do you know how much use my EP has had  

I asked for advice on my star diagonal not for my lens cleaning to be scrutinised ?

"I haven’t noticed this before it’s only the 3rd time I’m going to use it."... remember?
You started about that yourself... It was just really good advice to not do what you did.

The same kind of beginners mistake probably caused the diagonal to get screwed (pun intended) Maybe you tried to move it in a better position without loosening it while observing...?

[Alfian]

I had a very similar problem with a Skywatcher 2" dielectric diagonal. Thinking it had just come unscrewed I tried to tighten it and made it worse. As far as I can tell they are not threaded but some kind of interference fit. I solved this by VERY CAREFULLY applying an epoxy liquid metal type glue to the open join and leaving it pressed together. This did the trick. For a while I was reluctant to use any heavy EP in it but it worked out OK.

[LukeSkywatcher]

Sounds like bare threads. If you want to move the diagonal around in the scope tube to get a comfortable angle to view, you should loosen the screws holding it in place. I used to turn one of mine while screws we're tightened. Completely stripped the threads. It was just a cheap one with plastic barrell.

Wrap some tape around the area that is stripped and it will be fine, once you remember to loosen the screws when turning the diagonal.

[Andy R]

21 hours ago, Waldemar said:

 

21 hours ago, Andy R said:

How do you know how much use my EP has had  

I asked for advice on my star diagonal not for my lens cleaning to be scrutinised ?

"I haven’t noticed this before it’s only the 3rd time I’m going to use it."... remember?
You started about that yourself... It was just really good advice to not do what you did.

 

 

Mein gott i remember just fine, if you ‘read’ the post again it was clearly stated with reference to a Di-electric star diagonal which is a upgrade to the standard diagonal thats supplied with the majority of beginner scopes. Which incidentally I have used a few more times for both daytime (nature watching/village life observing) and nighttime observing with no wobble issues. I guess the issue is more build quality than my actions  

With regards to lens cleaning, I keep my scope erected by the back door at all times(no pun intended) minus lens and diagonal. However if friends or family visit it’s a good conversation piece  and usually I pull out the lens and standard diagonal and give them a look. On this occasion my lens had been human handled and had acquired a smudge from a stray finger and hence required a clean. Without appearing to be too horrified and obsessive I put the lens away to be cleaned at a later date which just so happened to be the other night.

 I’m a strong advocate of search and research before asking repetitive questions on forums and so well aware of do and don’t with lens/scope cleaning but not so with the internals of said star diagonal. 

Anyhow I thank you for your advice and is duly noted ??

[Alfian]

7 hours ago, LukeSkywatcher said:

Sounds like bare threads. If you want to move the diagonal around in the scope tube to get a comfortable angle to view, you should loosen the screws holding it in place. I used to turn one of mine while screws we're tightened. Completely stripped the threads. It was just a cheap one with plastic barrell.

Wrap some tape around the area that is stripped and it will be fine, once you remember to loosen the screws when turning the diagonal.

When I had the issue with the SW dielectric diagonal, it had been used correctly and not had particularly heavy EPs used with it. The problem became apparent when diagonal and EP were rocking just very slightly in the scope. I could not find any swarf or other evidence that any threads were stripped in fact my initial thought was that the barrel was held in place by an internal locking ring which its not. If any existing  threads were stripped then I guess it must have been poorly cut in the first place. Whatever, as said, curative treatment was applied but I wouldn't be in any bustin' hurry to buy another if I had to.

[Louis D]

I would stick with GSO/Revelation diagonals.  I know they screw securely together.  I read some reviews of the SW diagonal also complaining about the tubes coming loose, so you're not alone.

[Waldemar]

Interesting test:

https://www.baader-planetarium.com/en/downloads/dl/file/id/160/product/2873/testreview_mirror_vs_dielectric_vs_prism_diagonal_comparison_w_paolini.pdf
and:
https://www.baader-planetarium.com/en/downloads/dl/file/id/293/product/2873/testreview_the_baader_bbhs_sitall_silver_diagonal_w_paolini.pdf