Which way do I move my secondary mirror?

[Space Cowboy]

As you can see from the image taken through a collimation cap the secondary mirror on my 10" DOB is not central with the focuser. The question is which way do I move the secondary to align it central with the focuser?

[skybadger]

I'll stick my neck out...

First I assume the sky is to the left and primary to the right. 

I would rotate the secondary long axis about 15 degs CCW to align with the tube direction unless it's the picture being taken at this angle...

Then I would increase the distance from the spider to move the centre of the 2ndary mirror towards the centre of the focuser view, along the tube axis.

[Space Cowboy]

1 hour ago, skybadger said:

I'll stick my neck out...

First I assume the sky is to the left and primary to the right. 

I would rotate the secondary long axis about 15 degs CCW to align with the tube direction unless it's the picture being taken at this angle...

Then I would increase the distance from the spider to move the centre of the 2ndary mirror towards the centre of the focuser view, along the tube axis.

Thanks, yes the scope is pointing left.

[Spile]

The most obvious error is c≠d which indicates tilt/rotation errors (https://astro.catshill.com/collimation-guide/) 

I would also expose the primary mirror as the reflection will give an indication of the error. See step 2 of the primary check.

[Space Cowboy]

43 minutes ago, Spile said:

The most obvious error is c≠d which indicates tilt/rotation errors (https://astro.catshill.com/collimation-guide/) 

I would also expose the primary mirror as the reflection will give an indication of the error. See step 2 of the primary check.

Thanks for that link, just what I was looking for!

This is the primary Image through the cap:

Edited August 24, 2023 by Space Cowboy

[Spile]

I tried to overlay circles on the second image but the edge of the focus tube was too undefined. Place a piece of paper (as per the link above) behind the focuser and take the photo through the cap again.

Meanwhile, this shows the secondary error from the first image...

Edited August 25, 2023 by Spile

[Space Cowboy]

4 hours ago, Spile said:

I tried to overlay circles on the second image but the edge of the focus tube was too undefined. Place a piece of paper (as per the link above) behind the focuser and take the photo through the cap again.

Meanwhile, this shows the secondary error from the first image...

Thanks, that's clearly defined. I've been looking for an overlay reticle/circle.  I'll do the primary shot again. 

Edited August 25, 2023 by Space Cowboy