Need help removing rings around stars

[George Gearless]

Hey guys.

After a long hiatus, I was out last night to have a go at the Triangle Galaxy.

After stacking in DSS, many of the single stars have a distinct halo/ring around them. At first I thought it was because all my images were equally out of focus. But upon inspection of the single photos, that wasn't the case. So It's got to be somewhere in the stacking process. But I have no idea where to look or check.

Has anyone encountered this problem themselves, and what did you do about it? Would really appreciate any help. 

 

 

 

PS: I've only made a quick 'wipe' in Startools just to make the picture recognizable.

[newbie alert]

Yep, sorry they're out of focus.. is the focusser slipping? What method did you use to focus initially 

[George Gearless]

12 hours ago, newbie alert said:

Yep, sorry they're out of focus.. is the focusser slipping? What method did you use to focus initially 

Ugh, I was hoping you wouldn't say that :(.

I use an electric autofocuser and the autofocus function in Ekos/Stellarmate. So at least initially I believe the focus was spot on. 'Initially' being the key word here. I have to admit that I did not refocus over the course of the photographing session. It just didn't occur to me that focus could be lost. The silly thing is, that you can set Stellarmate to check focus between one or several images. As it turns out, that function is there for a good reason. So I'm realy kicking myself here.

I've just realized that the pictures I checked, were the first 2 or 3 of overall 50. And they looked fine. Which was why I thought some wrongdoing in the stacking process. But when I get home from work, I'll check the last ones. I suspect they'll prove you right.

This is a lesson I'd rather have learned without wasting a whole evening/night. Oh well :).

 

Thanks for your reply. Even if you were the bearer of bad news.

[newbie alert]

Sorry to hear, it might be worth checking your focusser or if the temp drop is drastic then refocus more often depending on setup

I don't personally refocus on a imaging run on either of my setups

[wimvb]

Even if it’s a focusing issue, you should still check your stacking parameters. Changing the rejection settings can improve the star shapes.

[George Gearless]

1 hour ago, wimvb said:

Even if it’s a focusing issue, you should still check your stacking parameters. Changing the rejection settings can improve the star shapes.

Sounds interesting. Change the rejection setting in what way?

 

[adyj1]

Out of interest, @George Gearlesswould you mind posting a single exposure with no processing? I'm interested to see a comparison between that and the stacked image, (given how blurred the stacked result is...) and might give me something to look out for in case this happens to some of my images in the future...

Thanks

 

[wimvb]

4 hours ago, George Gearless said:

Sounds interesting. Change the rejection setting in what way?

 

You will probably need to relax the rejection criteria a bit. As always: experiment. 😁

[George Gearless]

17 minutes ago, adyj1 said:

Out of interest, @George Gearlesswould you mind posting a single exposure with no processing? I'm interested to see a comparison between that and the stacked image, (given how blurred the stacked result is...) and might give me something to look out for in case this happens to some of my images in the future...

Thanks

 

Absolutely.

At work at the moment, but will do so when I get back home (about 5 hours from now).

[happy-kat]

Also the settings on the cosmetic tab when used can cause the centre of stars to be removed

[George Gearless]

As requested by adyj1 , here is first the stacked result after having been run through DSS. It's as is. Only stacked, nothing else (  but with 35flats, 100bias, and 25 darks). 24,3 MB.

Keep in mind that I have used default settings for DSS. I don't know what half of it means :). The rings are clearly visible on the final stacked image.

 

Autosave.fits

 

Secondly, one of the frames from the 50 piece photo session. 0 Gain, 120s exposure, guided. 4,1 MB. You'll notice the absence of rings.

 

M_33_Light_055.fits

 

A bit of data, in case it's usefull: 

AP 80/600 EvoStar ED

ZWO 385MC camera

ZWO Electronic Auto focuser

Stellarmate/Ekos

 

Edit: Just wanted to add that I intend to spend the evening fiddling around with different settings on DSS to try and get a different result. I was a bit desolated initially when told that they're out of focus. Because that sounded like a believeable theory. But I've checked most of the pictures and none of the single pictures contains rings. It's only after stacking that the rings appear. So I'm cautiously hopeful that I during the course of this evening will have figured out what causes it. I'll report back if I find anything. If anyone has any suggestions apart from those already given, I'd sure appreciate a hint or two and hopefully cut off an hour or two of setting trial and error.

 

Edited September 6, 2021 by George Gearless

[wimvb]

24 minutes ago, George Gearless said:

Edit: Just wanted to add that I intend to spend the evening fiddling around with different settings on DSS to try and get a different result. I was a bit desolated initially when told that they're out of focus. Because that sounded like a believeable theory. But I've checked most of the pictures and none of the single pictures contains rings. It's only after stacking that the rings appear. So I'm cautiously hopeful that I during the course of this evening will have figured out what causes it. I'll report back if I find anything. If anyone has any suggestions apart from those already given, I'd sure appreciate a hint or two and hopefully cut off an hour or two of setting trial and error.

That definitely sounds like it's the rejection settings in dss. I've had this with pixinsight sometimes, and adjusting the rejection parameter for high rejection, solved it.

[George Gearless]

Success! 

In 'Stacking Parameters', the tab named 'Cosmetic' I unchecked both boxes that say 'Detect and clean hot/cold pixels'.

I've got nice circular stars now after stacking. This is just a jpg from Fits Liberator. Didn't even run it through Star Tools. Just wanted to post that the problem was solved. And yes, I've noticed the satelite track (how can you even miss that). I'll identify the picture later and leave it out of the stack. Point of interest here is the stars and their missing rings. Not the picture as such.

Thank you to everyone who participated in the search (especially wimvb and happykat).

 

Now for the long arduous task of running it through Star Tools properly and see how good an image I'll be able to glean from the data.

 

 

 

 

Edited September 6, 2021 by George Gearless

[happy-kat]

On the startools site there is a tutorial for the optimum DSS settings to use for StarTools.

https://www.startools.org/links--tutorials/starting-with-a-good-dataset/deep-sky-stacker-settings