Another weird cdk star halo issue!

Chris White- Overcast Observatory · Sep 5, 2025 at 01:21 PM

Try shooting without a filter (if you have one in the optical path).

If the filter is causing it, the further off axis you are the more offset the halo will be.

andrea tasselli · Sep 5, 2025 at 07:59 AM

Not sure about a CDK but in other compound systems with spherical or quasi-spherical surfaces I'd suspect a lateral shit of the secondary relative to the primary.

Going through my images I just recently took , it looks like this only happened with my red and blue filters and the skew was at different angles between them both?? The blue is the one in the image I posted here where it faces bottom left and the red had it top left.

On my LUM and other filters it doesn’t show up at all.

Starting to think it may be a reflection?? All my data from my WR134 integration seemed fine it was only the latter half of my 7217 data where the moon was low on the horizon where it showed up…I think??

andrea tasselli · Sep 5, 2025, 02:15 PM

Better post a full field image but I don't think this being a reflection issue.

here are a couple frames from my blue filter on 2 different images one is a complete stack the other two are single.

I even noticed this on my red frames with this most recent project where when I finally combined my RGB I got weird star halos that showed different flares of red and blue in different directions.

After looking over multiple nights, I think this is temp related still. I had this issue before the scope had to be sent back because of other issues that they eventually had to redo both mirrors to fix.

Look how different the halos look between different nights.📷 stack.png

maybe I should see what happens if I run my fans at 75% vs 100% and check the aperture ring is bulging enough to let air pass more because this looks like boundary layer issues if I’m not mistaken from my earlier troubleshooting

andrea tasselli · Sep 6, 2025, 11:39 PM

If the direction of the flare is in the vertical direction then yes, this could be an issue with thermal plume. But if the different filters were used across the night then why you wouldn't see on some and you would on others?

yea, it isn’t on my lum filter frames at all!! really confusing, I thought maybe tilt also, after running some image analysis it seems I have some minor tilt

Dark Matters Astrophotography · Sep 7, 2025, 01:01 AM

Anthony Grillo · Sep 5, 2025 at 12:38 AM

I just recently got my brand-new scope back from planewave after a couple months, they had to refigure both mirrors entirely unfortunately!!

While everything seems to be working tons better than it was before I’m still getting some weird star halos. Mind you now, I still think I need to tweak collimation a tad but I’m not so sure that is the issue here.

The halos of brighter stars seem to skew toward the left/bottom left of my images and is the case with most bright stars across the frame. Anyone have any idea as to what could cause this??

📷 Cntest.png

We run the fans on our CDK20 only when not imaging, and at 100% during those times. During imaging we shut them off, as we see issues like this if we have the fans running during imaging.

This is something we are working on a design to solve, as not running the fans at all during imaging is not ideal, however it does improve star quality over what we get when they are on at all.

Thank you!! I will for sure shut them off after cooling down when I image tomorrow, honestly that’s the only thing I can think of that will cause weird halos that change shape from night to night.

By the way, love your work! your images are some of my favorites!

Dark Matters Astrophotography · Sep 7, 2025, 01:29 AM

Anthony Grillo · Sep 7, 2025 at 01:20 AM

Thank you!! I will for sure shut them off after cooling down when I image tomorrow, honestly that’s the only thing I can think of that will cause weird halos that change shape from night to night.

By the way, love your work! your images are some of my favorites!

Thank you!

Feel free to hit me up in email or DM here once you get some tests done with the fans off.

I got a bunch of clear nights up ahead so I should be able to test tomorrow!! I am going to tweak collimation too because it seems I may be slightly off