colimation problem.

[mahmud]

I am a beginer in this area. I bought a scope slywatcher 250 p very recently. To test my laser colimator I de colimate my scope. Now I am trying to fix it using colimation cap. After study I try to align my secondary mirror with my focuser which image is given here. I am confused is it rightly aligned with focuser or not. If it is not, please give your valuable opinion what the image shoud be if secondary mirror is correctly aligned with focuser. Thanks in advance.

Edited December 25, 2021 by mahmud

[Ricochet]

The secondary needs to move "down" in your picture. You want the gap between the edge of the focuser tube and the secondary mirror to be the same all the way around. If you have a sight tube (included in long cheshires) or concenter you can more easily see where the secondary needs to be using either the edge of the sight tube or a ring with the concenter. 

[mahmud]

5 minutes ago, Ricochet said:

The secondary needs to move "down" in your picture. You want the gap between the edge of the focuser tube and the secondary mirror to be the same all the way around. If you have a sight tube (included in long cheshires) or concenter you can more easily see where the secondary needs to be using either the edge of the sight tube or a ring with the concenter. 

Thanks

[mahmud]

1 hour ago, mahmud said:

 Thanks a lot. Can u share the image of a secondary which is perfectly aligned with focuser, then I can do colimation at my end based on that image. Thanks in advance.

 

[Spile]

This will show the checks. https://astro.catshill.com/collimation-guide/
A Cheshire eyepiece and sight tube combination tool will make it easier to check the concentricity . 

[Pixies]

On 25/12/2021 at 09:53, mahmud said:

Thanks a lot. Can u share the image of a secondary which is perfectly aligned with focuser, then I can do colimation at my end based on that image. Thanks in advance.

Here's one from my dob a while back - using a phone camera down a collimation cap:

 

The reticle is superimposed using the 'Mire de Collimation" application form this page (scroll to the bottom): 

http://sweiller.free.fr/collimation.html#:~:text=Also try to superimpose the image coming from the webcam with this freeware from Gilbert Grillot

Note: this is for a Windows PC/laptop

 

It's much easier using a long Cheshire / sight-tube. You can align the secondary much more easily when the reference circle is closer:

and even closer! There is a very thin gap visible around the outside of the secondary: