SCT off centre secondary??

[Jammy]

I've been attempting to image galaxies with my C9.25 rather than my 80ED to increase image scale, but my stars look like they're trailing slightly and I'm wondering if this is down to an off centre secondary mirror.  I did accidentally rotate the secondary mirror over a year ago, but I've not used the scope until recently.

I've attached an image of a de-focused star that I've used for collimation (near the zenith).  In this image should the spot within the collimation rings be central rather than over to one side?

Is this the result of an off-centred secondary mirror?

I've taken 10 second shots of star fields and they still show slight comma , but don't see how this can be down to tracking error in such a short period of time.

Has anyone seen this before?  Thanks for any help you can offer.

 

[RT65CB-SWL]

I would have thought that if your collimation was off/out, then the disc would have been slightly oval/squashed to one side. I had the same with my C6/SCT-xlt a few years ago.

I don't know whether Rother Valley Optics have the facilities to do it. I think they are your nearest reputable dealer. Otherwise a long day and drive as you may have to bring it down south to SCTelescopes.

This may help---> https://www.youtube.com/watch?v=hqRVIDj4aZA (other videos are also available).

 

 

Edited June 15, 2020 by Philip R

[Jammy]

Do you think there is something out of alignment?

I was thinking about taking it to a specialist, but not sure where to find one in this part of the country.

[Alkaid]

I can see that with the star de-focused you’ve got nice collimating rings. What’s the pin pointy spot in the middle?  (You normally don’t get that in a de-focused image).  Cheers.

[Jammy]

Good question!  I thought it was reflections of the focus star, but I've been told by someone in another forum that it is called a Poisson spot.  All to do with light waves.

I've looked it up and there does seem to be something in this.  I did an internet search and ended up on Cloudy Nights where there were a few threads about how the spot should be central, and if it isn't your scope is out of alignment.

Honestly, I don't know what to believe.  All I know is that my scope is showing good shape stars in some areas, and not others.  They're not terrible, but noticeable when imaging.  I was wondering if anyone else here had ever seen this, and if it was a problem, then how to correct it.

Does anyone know a good scope doctor?

[Martthebass]

Have a word with Adam or Ian at RVO, they’ll be able to assist I’m sure. Quite local to you (assuming you’re Scunny or thereabouts).

[Jammy]

11 minutes ago, Martthebass said:

Have a word with Adam or Ian at RVO, they’ll be able to assist I’m sure. Quite local to you (assuming you’re Scunny or thereabouts).

Thank you.  I've been to and bought astro equipment from RVO, but wasn't sure if they would help with this sort of thing.  I'll give them a try.

I'm a little further than Scunny, but still my nearest astro specialists.