Eliminating focuser slop in laser collimation

[Giles_B]

I'm quite happily getting on with a 10" Orion XT10i and getting some great views of the night sky on the odd occasions when it is clear!

The XT10i seems to lose collimation rather readily, so much so that I can get it nicely collimated in the day only to find it has lost some collimation at night. After mucking about with a torch for a while, a couple of months ago, with a view to being able to collimate easily in the dark, I invested in a laser collimator (specifically a  Baader LaserColli Mk3 https://www.365astronomy.com/Baader-LaserColli-Mark-III)

I find this does allow me to do night time collimation very well and night time views are now more consistently good - however I have noticed that my focuser allows the collimator quite a lot of movement and, when collimating the secondary, the laser mark moves on each insertion of the collimator. Further investigation shows it can be wobbled around quite a bit - from bang in the centre of the centre mark on the primary to about 30-45 mm offset from the mark. I'm pretty certain it is the focuser not the collimator, as I can physically feel the collimator moving when I apply pressure to it. All told, collimating to this quite variable point doesn't seem to have a negative effect on the views. Doing so in the light and checking the view of the primary with a collimation cap shows that there is a view of all the primary clips, although the view can be a bit eccentric within these limits. But overall to my eyes I can't see a substantial negative effect on the view quality of the night sky. However, the wobble is a bit annoying, and I'd love to improve the stability of the LaserColli in the focuser and stop messing about with my secondary quite so often.

Besides replacing the focuser - which is an eventual plan whenever I both have funds and Baader Diamond Steeltracks come back into UK stock - as the collimator has a 1.25" barrel, I wondered if replacing the 2"-1.25" reducer to one of a higher quality might be helpful.

Has anyone had a similar problem and how would they recommend I solve it?

 

[Second Time Around]

I encountered the same problem and solved it with a Glatter parallizer.  This allows 1.25 inch eyepieces and lasers to be fitted into 2 inch focusers and hold them without slop.

It works very well with my Baader Diamond Steeltrack and my Hotech laser.

[Giles_B]

Just looked up the Glatter Parallizer on FLO - that's a great tip. I notice it is threaded for 2" filters, so I presume it won't take a 1.25" eyepiece with a filter in place if I use it for viewing?

Edit: Further investigation shows it is out of stock everywhere in the UK and EU which is disappointing. Definitely one for the wish list though...

 

Edited May 3, 2022 by Giles_B

[Second Time Around]

There's no problem with using a 1.25 inch filter and eyepiece.  I just tested it though to make sure.

An ad here on SGL or UK Astro But/Sell may get you a pre-owned Parallizer.  Good luck!

[Ricochet]

You need to work out which part(s) of the focuser is causing the wobble. If the issue is in the draw tube or 2" clamp a better reducer won't help. 

[Giles_B]

25 minutes ago, Ricochet said:

You need to work out which part(s) of the focuser is causing the wobble. If the issue is in the draw tube or 2" clamp a better reducer won't help. 

I guess moving the focuser in and out is the way to see if the draw tube is causing the problem. Is the best way to distinguish between wobble caused by the 2" clamp and that caused by the reducer to check the play in a 2" vs a 1.25" eyepiece? Or is there something more scientific I'm missing?

[Ricochet]

If it isn't readily obvious when you push on the collimator all I can think of off the top of my head is to tighten and loosen the different clamps and to watch for which ones lead to a change in the position of the laser dot.

With my bresser dob I had a problem when I upgraded the reducer to a Clicklock because the 2" clamp was almost entirely a compression ring and the reducer had an undercut, which meant the reducer would be tilted as the compression ring tightened. I upgraded the 2" clamp to solve the problem, but the parallizer would have also solved the issue if I was only concerned about 1.25" eyepieces. 

[Giles_B]

Just by way of an update, a couple of minutes fiddling showed this was definitely a problem with the reducer rather than the 2" clamp or the draw tube. Fantastically, the SGL wanted post was very kindly answered by a fellow with a Glatter Parallizer to spare. This arrived today, and works a treat. The collimation with the parallizer in place was about 20mm off the mark on the primary - so, not insignificant - and what is more, when I adjusted it, removed and reinserted the LaserColli, it stayed dead centre.

I was so delighted I tried it about six times in a row - perfect every time. My partner really couldn't get her head around why I was so overjoyed 🤣

So - a really big thanks to the SGL community on every front for some great advice and for being willing to help out and part with equipment to boot. I'm a bit lost for words actually, so some mild emoji-ing will have to do 😃😄😁

[Ricochet]

Great news Giles. If the collimation was that far out you will probably notice an improvement the next time you use the scope.