Another is it collimated correctly thread....

[hms_furious]

Hopefully the photo is clear enough. This is a 150i so the primary is NOT collimateable. 

My daughter moved the secondary quite considerably to the point it was more a sausage than a circle so it has been a learning curve!

I think I have the secondary in a nice circle and centred. The doughnut on the primary is in the centre of the collimating eyepiece. 

Does it all look ok? The bit that is niggling is the bottom seems to have quite a wide gap but moving it up or down takes the centre off of the doughnut.

What do I do!? Having dreaded doing this and it taking much longer than no doubt it should, I have no idea anymore! 

Thanks all, again.

[Pixies]

It's hard to say from that photo. Certainly, The eyehole (small black dot) is not inside the doughtnut.

As you can't adjust the primary, your aim to make sure the secondary is correctly aligned, is to centre the dot inside the doughnut.

Are you using a Cheshire? It looks like there is a cross-hair that's out-of-focus. You can use this to make sure the secondary is correctly positioned under the focuser and that it's rotated correctly. It's a little easier to do that if you use coloured paper behind the secondary and also between the secondary and the primary. It'll give you a view like this:

Then with a Cheshire/sight-tube, you can make sure it's aligned under the focuser correctly, by adjusting the secondary so that it is perfectly concentric to the end of the sight-tube:

 

If you find that the secondary has been (mis)adjusted a lot, there is a good way to 'reset' it: 

Keep loosening the 3 adjuster screws and tightening the centre screw. This brings the mirror back up the tube, away from the primary. Keep doing this until the mirror has been pulled all the way back to the top of the tube and is flush against the vane-assembly, with the adjusters just barely loose. This means that the base of the secondary holder is now flush with the assembly. Now you can bring the secondary back down the tube by loosening the centre screw by a turn and taking up the slack with the adjusters by screwing them all in by equal amounts. If you repeat this until the mirror is directly under the focuser, making sure the 3 adjusters are always rotated by equal amounts, you can be sure that the secondary mirror is not tilted. Now, all you need to do is make sure it is rotated and facing the focuser correctly - so that the image of the secondary is concentric as above. Then you can take out the paper and make a final adjustment of the secondary tilt. As you can't adjust the primary, just look to put the dot inside the doughut.

 

Does that all make sense? Drop me a PM if you need a hand.

 

 

[hms_furious]

This is where I have got to so far thanks to Pixes help. 

[jonathan]

I fretted and worried over my own secondary (and briefly, primary) collimation for months, it sat in the end room collecting so much dust...

The best thing to do is get outside when the stars are visible and perform the star test (Polaris is the recommended star, easy to find and doesn't move), look for concentric rings around the de-focussed star using a high power eyepiece, if it's obviously off-centered then do more adjusting.  Looking at your photos I think you'll probably find it's good enough for visual use.

[Spile]

On 28/03/2021 at 10:50, jonathan said:

The best thing to do is get outside when the stars are visible and perform the star test (Polaris is the recommended star, easy to find and doesn't move), look for concentric rings around the de-focussed star using a high power eyepiece, if it's obviously off-centered then do more adjusting.

I adopt the same "star test first" technique.

I am sometimes tempted after a few cloudy nights to play with my secondary mirror but I am seeking help for that condition.  

[Pixies]

1 hour ago, Spile said:

I adopt the same "star test first" technique.

I am sometimes tempted after a few cloudy nights to play with my secondary mirror but I am seeking help for that condition.  

The secondary shouldn't need adjusted very often at all. I'll only check it after transporting the scope.

I will check the primary every night (while I wait for it to cool down). But it only takes 30 seconds and need adjusting very rarely.