Collimating an f5 Newt - advice

[SuburbanMak]

Hi posting this one here as I am a complete newbie as far as these reflect-y things go…

I followed the Astrobaby blog advice on collimation steps - photo 1 shows what I had at the end of tweaking the secondary. 

Photo 2 shows all 3 clips visible and the centre dot of the collimation cap sitting neatly in the centre circle on the mirror. (Both also aligned with the Cheshire crosshairs but didn’t manage a photo of that). 

The reflection of the whole collimation cap is off centre however. Does this matter and if so what should be my next move bar starting from scratch?  

[malc-c]

To my eye that is still out of collimation.  It looks like you are near step 1 in this guide

This is what you are after

[Pixies]

I would say that the secondary mirror is slightly twisted. you'll need to sort that out first.

 

you can also see that from the reflection in the second image:

The above light-blue ellipse shows the outline of the offset secondary. It should be inline with the focuser, once the secondary if facing it correctly. More like:

 

 

[SuburbanMak]

This is incredibly helpful - thank you both!

[Spile]

I am seeing rotation error. Aim to get c=d https://astro.catshill.com/collimation-guide/

[SuburbanMak]

I think I am getting there. Thanks for all the advice & links. 
Managed to get the laser working by taking it apart and putting it tightly back together again and have got on better with a collimation cap/laser combo than I was with the Cheshire - my spatial awareness isn’t brilliant and I find it quite hard to make sense of the crosshairs vs. the spider vains. The laser (which I checked collimation by firing through a 60mm refractor at a wall 5m away and confirmed the spot stays still when I rotate - childishly enjoyable stuff!) is a bit more intuitive.  Got things lined up to best ability using the collimation cap then went back and forth between secondary & primary screws until I had the dot in the primary’s centre circle and disappearing down the centre hole. View now looks as below, not much chance of a star test tonight however… 

Edited April 10, 2022 by SuburbanMak

[malc-c]

It's difficult to advise as we don't know the plane of the optical axis from these images, as the camera may be at an angle to it and thus is making the collimation look off.

Using a clock face as a reference, looking at the shadow the axis is running through 10 O'Clock position.  If so then it would seem you have sorted out the secondary rotation mentioned above, but something is still not quire right as the reflection is still bunched up in that direction.  If the optical axis is through the 3 to 9 O'Clock  (ie horizontal) in the image then there is still rotation.

Have you checked that the focuser is square to the tube, and that the laser is hitting the centre line form the spider ?  It's been a while since I set up the optics on my scope and I used a length of threaded bar securely bolted through the spider (having removed the secondary) and then once the focuser housing is square adjust the spiders so that the secondary mount is such that the laser hits the centre of the bar.  It is often a case that you can get the optical axis collimated, but out of alignment if you follow - Best image I could find and modify below (focuser misalignment grossly exaggerated!)  

Having said that, I'm not the best person to comment on collimation, although when I had an issue with the scope years back I must have recollimated well over twenty times even stripping the scope right down on one occasion.  I even purchased a self centring eyepiece adapter to ensure the Hotech laser was centred as using the traditional holder with thumb screws can cause the collimation to be out of alignment.  Final test is the start test, which hopefully gives you nice concentric airy rings

[Spile]

This is my interpretation of your alignment. This is assuming no camera parallax error.