Do I have Coma Abberation? Elongated Stars

[kgunessee]

Hi guys,

 

I need some help with my imaging! I have recently purchased a Skywatcher 130PDS and SW Coma Corrector, however I am getting elongated stars in my images (see attached).

The coma corrector has 55mm of backfocus, and sits in a train as follows - focuser > CC > OAG > Filter Drawer > ASI533MC Pro Camera.

As you can see in the image, the brighter stars are not so much of an issue however the smaller stars are. Collimation is fine, as is focus.

Could this be a spacing issue, coma, or something else? I'm at a loss! Any help would be greatly appreciated.

Image details:

• 1.5hrs
• 120s Subs
• L-Pro Filter

[vlaiv]

8 minutes ago, kgunessee said:

Could this be a spacing issue, coma, or something else? I'm at a loss! Any help would be greatly appreciated.

Given your setup - I think it is probably some sort of tilt in optical train.

Bottom right corner is the least affected (best looking stars) while opposite corner is the worst.

It could be that too much weight is hanging of that focuser, or maybe you should check if everything is square before clamping things down.

[kgunessee]

Hello, 

Thanks for your reply. I'll check this out, however CCD inspector only shows a tilt of 14%, so I'm not sure if it's this.

 

[Clarkey]

Whatever it is, it's not coma. Either tilt as @vlaiv suggests or possibly a collimation issue. My money is on tilt. If you are using the standard focuser there is every likelyhood.