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Collimation and Star-hopping

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Hi guys, 

I am new in the hobby. I figure it's best if I ask here rather than creating a whole new topic.

I got a nice second-hand skywatcher skyliner 8" Dob. 

I was wondering if my secondary collimation is good enough before I start collimating the primary.

1- To me it looks like the secondary is not fully centered on the focuser, it looks like it is slightly more towards the primary. The holder of the secondary doesn't help to fully assess this. 

2- The black offset of the secondary is somewhat off too, so the secondary is not fully facing the focuser in the Y axis, or am I being too perfectionist?

3- The primary seems to be centered in the secondary, I can see the three clips of the primary, or it isn't good enough?

I had a cracking look at the moon last night for the first time with the collimation you see in the picture and it was awesome.





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I have the 200P and this is what I do...

Using a simple cap (an eyepiece cap with a 1mm hole in the centre and a shiny washer glued to it) check the secondary is a centred. I had to tweak my secondary slightly using the three allen screws and the central screw. It hasn't moved since.

For the primary, looking through the cap I make sure the "polo" is between the cross-hairs. Your looks slightly out but I would check the secondary with a cap to make sure that is central first.

Finally and most important, I do a star test to ensure everything it spot on.



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Thanks @Spile, those are the spider vanes. I am using a simple cap at the moment as that is all I have. To put the "polo" in the middle of the cross-hair I'd need a barrel with cross-hairs. I was thinking about buying a cheshire. 

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OK. If you want to be fussy:


You could get the secondary centred more accurately, but it's really not bad. The secondary is aligned to the primary well (all 3 clips showing).

However - you need to adjust the primary collimation so that the black dot (eye hole) is inside the doughnut.


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Welcome! And congrats for your acquisition!

Pixies has 100% nailed it.

I would also try wiggling/rotating the focuser tube and the cap around a bit to see if that might be the culprit here (which is typical).

By the way, here is the dedicated thread on the SGL for your scope: 



Edited by AlexK
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@Pixies That's a very neat tool. I'll use it too. Visually I could tell the secondary wasn't fully centred. I'll sort that out. The primary is clearly off too, just wanted to fine-tune the secondary (the most difficult part in my experience) before adjusting the primary. thanks a lot the feedback.

@AlexK Cheers Alex. I did try that. I wiggled the focuser tube and seemed pretty solid in place. Rotated the collimating cap, the view didn't change in any discernable way to my inexperienced eyes. Maybe the little whole in the cap is pretty well centred.  

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