Circular artifact in WBPP processed image, suspect flat frame issue - Forums

Topic starter

3 days ago

Hi everyone,

I’m seeing a circular artifact in my image after running WBPP. I used dark frames and the attached master flat. The artifact closely matches the flat frame, so I suspect it may be an issue with my flats. If that’s the case, I can reshoot a new set.

For this image, this issue occurs on all of my filters.

Any suggestions would be appreciated.

Thanks!

📷 Screenshot 2025-09-29 at 16.37.37.png📷 Screenshot 2025-09-29 at 16.38.15.png

Well Written

andrea tasselli

Frequent contributor

3 days ago

You have severe vignetting, that's all.

Catalin Iordache

Topic starter

3 days ago

Hey Andrea! Thanks for replying. Yes, I do have some vignetting, but I would expect flat frames to fix that. Here is another picture that shows better the ring/gradient I am writing about. I am not sure if this is because my flat frames are bad or maybe my dark frames have an issue. I already applied DBE and Gradient Correction, but the result is still bad.

📷 Screenshot 2025-09-29 at 22.36.26.png

andrea tasselli

Frequent contributor

3 days ago

Flats correct up to a point. If the loss is too high they are never going to replace the actual signal. Have you actually measured the light loss at the corners?

Brian Puhl

IOTD Staff

Frequent contributor

3 days ago

Flats should correct most vignette. If not, then i’d start chasing a light leak. First step i’d recommend is using bias instead of darks. If that doesn't alleviate the issue, the start shining a flashlight around your scope while looping exposures.

Catalin Iordache

Topic starter

2 days ago

@andrea tasselli @Brian Puhl Thank you for comments. I did re-shoot my flats last night. I forgot to move the focuser close to focus position while acquiring the initial batch of flats. The problem is now gone.