Colomation

[Andy67]

Hi guys.

For the first time since getting my pre loved XT8 I decided to check the colomation, it appeared to be out. I've had a go at adjusting the primary but haven't touched the secondary. I've attached a screen shot taken through the colomation cap, does this look right or am I off. I've tried looking for YouTube videos on how to use a Cheshire which I recently purchased but couldn't find anything that made me feel confident enough to use it so I reverted to the colomation cap.

Thanks in advance.

[dweller25]

Your collimation is close, you have some secondary tilt in the North to South direction in your photo probably because the secondary is not central under the focuser - it’s too high in the North direction. But that could be camera placement ?

Edited December 30, 2021 by dweller25

[Andy67]

Thanks David. I'll have another look and if it is out I'll have a go at adjusting the secondary. I take it you mean the difference between A & B ?

Edited December 30, 2021 by Andy67

[dweller25]

Yes, thats the secondary tilt, but first you need to get the secondary central to the focuser…..unless its a camera position issue

Edited December 30, 2021 by dweller25

[alacant]

1 hour ago, Andy67 said:

the difference between A & B

Hi

Be sure to read the common collimation myths  and the no nonsense explanation of collimation. 

You're quite close as it is so to hit the ground running...

• Make sure the spider vanes are all of equal length. 
• Now adjust C = D and E = F.
• Now you can rotate the secondary and tilt the primary to get A = B.
• Then use a Cheshire sight tube -preferably one with cross hairs- to perfect it.

Repeat the whole process until you're satisfied/bored.

HTH

 

Edited December 30, 2021 by alacant

[Pixies]

If you follow a guide like the Astro-baby one, they often suggest using coloured paper behind the secondary and down the tube, to help you determine the alignment of the secondary under the focuser. You then need to get it something like:

[Andy67]

Thanks everyone for your input. I'll have another look after work tomorrow night and see how I do.

[Spile]

The only thing I would add to the above is a recommendation not to put paper between the secondary and primary. As you can see from secondary step 2, the direction the dark of the offset secondary reflection is a useful check. https://astro.catshill.com/collimation-guide/
A Cheshire eyepiece and sight tube combination tool will have cross hairs than can confirm that your secondary is centred but although it’s worth spending time to get the secondary as good as you can, the priority is the alignment of the primary.

[clafann1]

nvm this post..

Edited January 4, 2022 by clafann1

[alacant]

28 minutes ago, clafann1 said:

couldnt have the second mirror fully show the primary.

Hi

Oh, desr. Maybe the secondary wasn't big enough. 

In any case, it doesn't matter. If you really do want to perfect it, wait until you can get along to an astro club. Meanwhile, concentrate on adjusting the primary. But don't spend too much time doing it. 

Remember that the secondary is just a flat bit of glass. Get it somewhere close. Then leave it.

But yes, if you want to do photography, cheap (all?) Newtonian telescopes need pulling apart and rebuilding with components fit for the task.

Cheers