Help Requested Identifying/Eliminating this Artifact

[GaryS]

Hi Folks
I was live-stacking last week and I barely spotted the artifact shown highly-stretched on the attachment. I'd never seen it before and have no idea what is causing it. Nothing has changed in my system but it has been a little while since I used Sharpcap. Also, the artifact may have been there earlier and I just failed to notice it. A knowledgeable friend suggests that it could be a 'stacking' artifact.

Anyway, I hope someone has encountered this before and can provide some information as to the cause and cure. Additional info bits include:
- OTA is PW CDK 12.5, F5.3
- Camera is ASI2600MM (clear filter in place at the time)
- Exposures are 30sec, Gain 100, Bin1
- Sharpcap 4.1.12693
- ignore the Starlink streaks junking up the image

Thank you for any clues or solutions!
Gary

[admin]

Hi,

two possibilities come to mind with that...

1) Something odd going on with flat frame correction (if you are using it). See if it goes away with flat frame correction turned off and then check that your flats are up to date and created according to the guide at https://docs.sharpcap.co.uk/4.1/#Gettin ... Correction

2) Frost or dew forming on the sensor or sensor window - if it's easy to do so, have a look at the camera sensor and see if it has a cloudy patch on it that could be frost or dew. Slower cooling might help, or using the window heater (if not already on), or potentially changing dessicant tablets (although that should be a last resort as it can allow dust into the sensor chamber)

cheers,

Robin

[GaryS]

Hi Robin & Thanks

1. No Flats or Darks in use
2. I haven’t been using the sensor chamber heater but the images appear pretty clear in all the images. Wouldn’t the images be somewhat blurred or affected ? The pattern artifact seems almost to be in the background but maybe the brighter target areas just upstage it.

So far, I’ve not been able to bring out the pattern with stretching on any .Fits files taken in the same session.

Is there any way this could be some kind of stacking artifact?
Happy Holidays!
Gary

[admin]

Hi Gary,

The only similar stacking artifact that I can recall was a case where the camera was colour, but the images were being stacked as if they were monochrome. The grid pattern in the raw images made a right mess in stacking with lots of weird fringes, but still nothing like that octagonal pattern.

How are you stacking, in SharpCap or in another application? In either case, since you have the FITS files, try stacking in a different program and see if the effect still shows... If it goes away then it's likely a stacking artifact in whatever you were using to begin with.

cheers,

Robin

[GaryS]

Happy Holidays Robin

A friend looked at a stack in Pixinsight versus SC. The artifact was only in the SC stack. It doesn’t appear in the individual frames or in stacks done in Maximdl or Pixinsight.

Regards & thanks very much for creating and so steadfastly supporting Sharpcap. It’s given great pleasure to so, so many astronomy lovers on this Planet.
Cheers
Gary

[GaryS]

BTW, I would be interested to know if there’s some aspect of the stacking/ image registration in SC could be going awry to cause this artifact? Should I be using another stacking mode other than ‘Default’?
Thank you
Gary

[admin]

Hi Gary,

in general, 'default' should be fine for most cases, and shouldn't introduce this sort of problem. If you can share the raw image files that produce the problem, I can run through the stack here and see if I see the same effect and/or spot anything else odd going on that might explain it.

cheers,

Robin

[GaryS]

Ok Robin, later today, I’ll post a link to a folder with some raw .fits images in my Google Drive. When these were stacked in Pixinsight by a colleague, there was no artifact. I can also include a .png stack from SC with the artifact. Let me know if there’s anything else that would help. Thank you.
Gary

[GaryS]

Hi Robin,
Here's the link to the "For Robin" folder in my Google Drive. you may have to request access also - not sure how to make it easier.

Once you are in the folder, you'll find:

1. processed with display stretch
- a single image stack
- a 60 frame stack

2. rawframes to stack - 68 raw fits frames

3. A single 9 frame, stretched image showing the artifact clearly

4. Here's the link to your "For Robin" Folder in my Google Drive:
https://drive.google.com/open?id=1-LYo- ... p=drive_fs


Thanks very much for you time and help with this pesky artifact!
Gary

[admin]

Hi Gary,

thanks for taking the time to put those resources together - looks like you need to approve my 'request access' request for me to be able to download, but I will catch up on that later.

cheers,

Robin