Skywatcher 130 PDS - Twisted Spider Vane ?

[spillage]

Have a look at the link below. I am just about to follow the same path.

 

[BrendanC]

Interesting, thanks for this. Should fix the pacman stars, but I wonder if it will also fix my spikes? I checked my vanes, they might have been slightly out, so now I need to collimate yet again. If that doesn't work then this could be an interesting way forward. Cheers! 

[Spaced Out]

On 02/12/2020 at 11:15, BrendanC said:

So, shout out to @Spaced Out if you're still around - did you ever resolve this, and if so, how?

I narrowed it down to focuser alignment/tilt (and possibly a very slightly curved vane ?). I tried to correct things by shimming the focuser, it helped but it still wasn't perfect. Then I was given another 130PDS ! I started using that instead and the other scope is now sitting in reserve.

Interestingly, looking around online I noticed a few other newtonian images showing the same sort of pattern, maybe it's not uncommon ?

[runway77]

I can observe some double spikes with my 150PDS as well. I have not yet identified what the problem could be. I suspect that my secondary mirror is not aligned well under the focuser. I have done the alignment using a collimation cap but that may not be enough for astrophotography. Have you tried to center the secondary mirror under the focuser? I have just bought this tool but I can't say whether it helps, it's been constantly cloudy here recently.

 

Edited December 11, 2020 by runway77

[Waldemar]

Don't you think that a great tool like this will work better if it is perfectly centered in the receptacle?
A nosepiece like the SCA adapter of Hotech would do the job a lot better then the screws in a standard holder to get this nice tool centered properly.

Edited December 11, 2020 by Waldemar
clarification

[runway77]

44 minutes ago, Waldemar said:

Don't you think that a great tool like this will work better if it is perfectly centered in the receptacle?
A nosepiece like the SCA adapter of Hotech would do the job a lot better then the screws in a standard holder to get this nice tool centered properly.

you are right, I do have a skywatcher twistlock adapter and I bought a 1.25 inch version of this concenter tool. The twistlock adapter seems to properly center my laser collimator in the focuser. The red dot ends on the same spot after I lock the adapter. I hope this would be the case with the concenter eyepiece as well. If this won't work, I will take a look at the sca hotech adapter.

[Spaced Out]

11 hours ago, runway77 said:

I can observe some double spikes with my 150PDS as well. I have not yet identified what the problem could be. I suspect that my secondary mirror is not aligned well under the focuser. I have done the alignment using a collimation cap but that may not be enough for astrophotography. Have you tried to center the secondary mirror under the focuser? I have just bought this tool but I can't say whether it helps, it's been constantly cloudy here recently.

 

Yeah last time I stripped the 130PDS I used a collimation cap to square things up. I now have the 2inch concenter so I may check it out again with that. I thought the concenter was quite expensive for what it is but I've found it fairly useful. 

[malc-c]

I had issues with my 200P producing extra spikes on bright stars.  The thread is now 8 years old so a lot of the images a fellow member (David Davies) posted to backup the theory are now missing, but the thread is still readable. https://stargazerslounge.com/topic/159748-200p-colimation-or-poor-optics/

In a nutshell the issue was caused by the way the secondary was silvered, in that the edges of the minor axis had flat sections where it was clamped and the silvering process was not able to fully coat the mirror.  For me the problem was resolved by using an oversized secondary, just a fraction over that of the one used in the 200PDS version of the 200 series OTA.  Now I know your scope is a PDS so it should already have a larger mirror, but if it has the same flats it might be contributing to the same issue.

The new mirror I had made by Orion Optics had no such flats on the minor axis

Now I'm not saying this is the case here, but it's worth checking the secondary, for size and if there are any flats on its minor axis.  It may mean recollimating the scope and pushing the primary closer to the secondary by a mm or two.  It's also worth measuring the secondary to confirm its dimensions meet the correct one for a PDS - No saying it they have fitted the standard P version, but its worth ruling out

Edited December 11, 2020 by malc-c

[Spaced Out]

14 hours ago, malc-c said:

I had issues with my 200P producing extra spikes on bright stars.  The thread is now 8 years old so a lot of the images a fellow member (David Davies) posted to backup the theory are now missing, but the thread is still readable. https://stargazerslounge.com/topic/159748-200p-colimation-or-poor-optics/

In a nutshell the issue was caused by the way the secondary was silvered, in that the edges of the minor axis had flat sections where it was clamped and the silvering process was not able to fully coat the mirror.  For me the problem was resolved by using an oversized secondary, just a fraction over that of the one used in the 200PDS version of the 200 series OTA.  Now I know your scope is a PDS so it should already have a larger mirror, but if it has the same flats it might be contributing to the same issue.

Thanks for this. I'll take a look at that too.

[runway77]

I too had a double diffraction spike problem with my 150 PDS. After I centered the secondary mirror under the focuser with the help of a concentre eyepiece and after I collimated the scope the problem was resolved. Additionally, I needed to buy a skywatcher twist lock adapter to ensure that my laser collimator is centered in the focuser. 

Edited December 27, 2020 by runway77