Collimation help

[Priesters]

Hi all, I'm pretty new to the world of collimation and need some help.   

Tools I have to hand are a Cheshire, a Collimation Cap and a Laser.  The scope is a Skywatcher 130 PDS. When I've convinced myself I've centred the secondary under the focuser tube usIng the Cheshire as a sight tube the laser misses the primary centre dot by a good inch or so and I get the same view with the Cheshire.  If I try to correct it using the collimation screws the outcome is awful.  After a couple of hours I gave up trying to centre under the focuser tube and the picture below shows where I am am up to now.  It looks to me like the primary and secondary are pretty square and the laser shows that too but clearly the reflection of the primary is (unsuprisingly) not centred in the secondary.  I think I can sort the 'front to back' misalignment using the centre bolt but I'm a bit lost about the side to side misalignment.  Do I need to adjust spider vanes to get this right or all there a whole host of other things going on that I'm just not seeing with my novice eyes. 

Any help would be much appreciated.  

Thanks

Andrew

[Buzzard75]

Looks like your secondary might have a bit of rotation relative to the focuser and that is what is most likely throwing off the position of the primary reflection. Also it appears to be a bit tilted to one side. I would start with this guide. Put something down the tube to block the reflection of the primary so you're not confused on what you're seeing when centering the secondary with the focuser.

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

[Priesters]

Thanks, I appreciate the response.  I had pretty much followed the procedure described in the link apart from the first bit about checking the spider vanes were positioned centrally.  I'll do that and follow the full procedure again and see where I get to. 

[wimvb]

In the picture which you attached to your post, try to identify what you see. The grey structure inside the red field, extending down, is the side of the secondary mirror. The black crescent on the left, right next to the white circle is the reflection of the tube wall in the secondary mirror. This shows that you have to work with rotating and tilting the secondary first. Forget about the primary until this is fixed. Once this is ok, you can start aligning the primary.

[wookie1965]

Try this it will make things easier did with me.

http://www.schlatter.org/Dad/Astronomy/collimate.htm

[Priesters]

Thanks for your help everyone.  

The picture below is where I'm up to now with my collimation efforts.  I added some nylon washers behind the collimation screws which really helped as the back of the secondary holding plate had become a bit dimpled. I can see from the photo that the secondary needs to go about 1mm or 2mm down the OTA.  Question I have is, what difference will that make?  I'm going to start EAA soon but definitely not full astrophotography.