Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
Get a Cloudy Nights T-Shirt Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu uh, User

Astrophotography and Sketching >> Beginning and Intermediate Imaging

Pages: 1
Gary Minder
member


Reged: 06/23/13

What is Causing This Star Defect? new
      #5979553 - 07/19/13 10:32 AM Attachment (24 downloads)

I am hoping somebody can tell me what might be causing stars to be so defective as seen in this tight crop of M13 from last night.

I have registered and stacked subs in DSS and PixInsight and see the same thing. I saw this same thing once in a set of subs I processed in DSS. I tried PixInsight with the same subs and it was gone.

I assume the culprit is some setting I am using. I just ran PI preprocessing, stopping at registration and there are no defects. I am working with 13 90-second subs. The PI integration setting I used are:

Pixel Rejection Algorithm: Windorized Sigma Clipping
Sigma Low/High: 4.0/2.0
Scale Estimator: Iterative k-sigma/biweight midvariance
Combination: Average
Normalization: Additive with Scaling
Weights: Noise Evaluation

Help! Thanks.

Gary


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gary Minder
member


Reged: 06/23/13

Re: What is Causing This Star Defect? new [Re: Gary Minder]
      #5979574 - 07/19/13 10:40 AM

As I look at that picture it almost seems like I am seeing a cross section of each star...like I've cut each star in half. Neat trick but not what I'm after!

Post Extras: Print Post   Remind Me!   Notify Moderator  
shawnhar
Post Laureate
*****

Reged: 06/25/10

Loc: Knoxville, TN
Re: What is Causing This Star Defect? new [Re: Gary Minder]
      #5979598 - 07/19/13 10:52 AM

I don't know about Pixinsight but I got something resembling this with DSS when my "clean remaining hot pixels" was set too aggressive.

Post Extras: Print Post   Remind Me!   Notify Moderator  
zerro1
Postmaster
*****

Reged: 08/02/09

Loc: Smokey Point , 48.12°N 122.25...
Re: What is Causing This Star Defect? new [Re: shawnhar]
      #5979628 - 07/19/13 11:15 AM

I don't have a clue based on the settings that you posted.

have you tried a different rejection algorithm other than windsorized? Like Min/Max or even no rejection to see if it will complete without the "defects"


Post Extras: Print Post   Remind Me!   Notify Moderator  
DaemonGPF
Redonkulous
*****

Reged: 03/22/08

Loc: Aurora Colorado
Re: What is Causing This Star Defect? new [Re: zerro1]
      #5979644 - 07/19/13 11:24 AM

Wait, I have a pic just like that. I know what it is. It's olive oil suspended in water!




Post Extras: Print Post   Remind Me!   Notify Moderator  
DaemonGPF
Redonkulous
*****

Reged: 03/22/08

Loc: Aurora Colorado
Re: What is Causing This Star Defect? new [Re: DaemonGPF]
      #5979650 - 07/19/13 11:26 AM

Seriously though - do you have a single, unstacked sub we could look at, and maybe the stacked, unprocessed version as well?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff2011
Pooh-Bah
*****

Reged: 01/01/13

Loc: Sugar Land, TX
Re: What is Causing This Star Defect? new [Re: DaemonGPF]
      #5979711 - 07/19/13 11:57 AM

I find that when I start messing with the DSS setting, I can get some weird stuff happening. In my case I was getting Stars with dark centers. I would set the DSS settings back to the defaults and try again. Also reviewing the DSS documentation is helpful. There may be some settings that you may have to change, but the defaults generally work. That is assuming the problem is with DSS. As Josh said we need to see the results of the stacking to be sure.

Edited by Jeff2011 (07/19/13 11:58 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
lawrie
Carpal Tunnel
*****

Reged: 01/31/06

Loc: Okanagan Valley
Re: What is Causing This Star Defect? new [Re: Jeff2011]
      #5979741 - 07/19/13 12:22 PM

I used to get that artifact with DSS also.

Post Extras: Print Post   Remind Me!   Notify Moderator  
RedLionNJ
scholastic sledgehammer


Reged: 12/29/09

Loc: Red Lion, NJ, USA
Re: What is Causing This Star Defect? new [Re: lawrie]
      #5980079 - 07/19/13 04:09 PM

DSS - Stacking Parameters - Cosmetic

Disable (uncheck) "Detect and clean remaining hot pixels"

Grant


Post Extras: Print Post   Remind Me!   Notify Moderator  
David Ault
sage


Reged: 09/25/10

Loc: Georgetown, TX
Re: What is Causing This Star Defect? new [Re: RedLionNJ]
      #5980432 - 07/19/13 07:53 PM

As Josh said, a single frame, or even better all the individual frames, would be very useful in figuring out what is going on. Both DropBox and Google Drive have free online storage (up to a certain quota) for sharing data, I'm sure there are others.

Honestly, the star shapes look like an out of focus star where the diffraction rings are visible, but since this is a multi-second exposure that seems unlikely.

This is just a guess, but another possibility is that some frames are being included that have no stars, or the stars are in a very different location, which will throw the rejection algorithms off. The edges of the stars are closer to the background level so they have a better chance of passing through the rejection algorithm while the peak of the star is thrown out. I see this same thing with plane trails when stacking with PixInsight, the central part of the plane's light path is thrown out, but as you move away from the center and the light level approaches the background level the pixels from that image are included in the stack leaving a double line effect.

Regards,
David


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gary Minder
member


Reged: 06/23/13

Re: What is Causing This Star Defect? [Re: RedLionNJ]
      #5980799 - 07/20/13 01:41 AM

Quote:

DSS - Stacking Parameters - Cosmetic

Disable (uncheck) "Detect and clean remaining hot pixels"

Grant




That was it. I ran DSS again with the "Detect and clean remaining hot pixels" disabled and there were no defects. Thanks.


Post Extras: Print Post   Remind Me!   Notify Moderator  
lawrie
Carpal Tunnel
*****

Reged: 01/31/06

Loc: Okanagan Valley
Re: What is Causing This Star Defect? new [Re: Gary Minder]
      #5981290 - 07/20/13 11:49 AM

Nice catch Grant.............well done.

Post Extras: Print Post   Remind Me!   Notify Moderator  
RedLionNJ
scholastic sledgehammer


Reged: 12/29/09

Loc: Red Lion, NJ, USA
Re: What is Causing This Star Defect? new [Re: lawrie]
      #5981558 - 07/20/13 02:49 PM

Thanks, guys. I knew because I'd been there

Grant


Post Extras: Print Post   Remind Me!   Notify Moderator  
sullij1
Pooh-Bah


Reged: 11/08/08

Re: What is Causing This Star Defect? new [Re: RedLionNJ]
      #5984289 - 07/22/13 10:52 AM

That was very useful. I have had that problem with DSS also.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1


Extra information
5 registered and 10 anonymous users are browsing this forum.

Moderator:  Knuklhdastrnmr, fishonkevin, WOBentley, rflinn68 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 576

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics