Strange stars.

[Jbro1985]

Hi there,

See attached preview. I am getting strange stars but not sure why.  I figured it was a collimation issue but just did a check using the "airy disk" and Als Collimation Aid and it seems fine...

Celestron C8, ASI1600mmc, ZWO EFW Mini, ZWO OAG (with ASI 185mc), guided through PHD2 and captured through SGPro.  Mount is an AZ-Eq GT6.  Any insights would be much appreciated.

Edit:  There is also a f6.3 focal reducer in the imaging train.

Edited August 26, 2019 by Jbro1985

[Jbro1985]

OK.  SO I think it might be sag...  Original Celestron thumb screw 1.25 visual back is not handling the weight of all the accessories.  Has anyone else had that issue and do they have experience of the William Optics Rotolock visual back as a solution?

[HunterHarling]

It is out of focus a bit, do you use a Bahtinov mask? It looks like regular SCT coma. If so, there isn't much you can do about it, aside from get a high quality reducer like the one Starizona makes.

Posting a full image might help diagnose the issue.

[Jbro1985]

I used SGP autofocus routine and have a pegasus focus cube. The image is very zoomed in.  I initially thought coma but it's the same across the whole image.

I'll share that later.