Rings appearing in lights

[Jonny_H]

Hi all,

Just looking through some of my first attempts at imaging from the other night and noticed that in my post-stacked images (prior to post-processing in PS) I have a few 'rings' showing up.  However looking at my original lights fits files I cannot see the rings in them.   Also looked closely at darks, flats and bias frames and cannot see the rings in these either. Photos attached.

Final image comes from APP where i stacked the lights, darks, flats and bias.  What am i doing wrong or is it just something hidden in the calibration files which i am not seeing?

 

Regards,

Jon

Edited March 1, 2021 by Jonny_H

[alacant]

Hi

Looks good.

The first image looks as if it has not had the flat frame processing. It shows dust on the sensor and vignette.

The second image has been processed with the flat frames and so the dust circles and vignette have been calibrated?

HTH

Edited March 2, 2021 by alacant

[Clarkey]

Looks like dust in the image train on a reducer, flattened or filter. It will be tricky to pick up on calibration frames but it should be removed by flats. You will only notice them on stacked images because they are so faint on a single sub.

[Jonny_H]

1 hour ago, alacant said:

Hi

Looks good.

The first image looks as if it has not had the flat frame processing. It shows dust on the sensor and vignette.

The second image has been processed with the flat frames and so the dust circles and vignette have been calibrated.

HTH

Its actually the other way around. The first photo is the stacked image from APP (not quite sure why the calibration frames didn't remove the vignetting - i'm still feeling my way around the processing side of things).

1 hour ago, Clarkey said:

Looks like dust in the image train on a reducer, flattened or filter. It will be tricky to pick up on calibration frames but it should be removed by flats. You will only notice them on stacked images because they are so faint on a single sub.

OK thank you. At the moment i have only the camera in the image train. I wondered if it was a light source finding it's way into the tube in somewhere but dust on the protective window could be the culprit. 

Edited March 1, 2021 by Jonny_H

[The Lazy Astronomer]

52 minutes ago, Jonny_H said:

Its actually the other way around. The first photo is the stacked image from APP (not quite sure why the calibration frames didn't remove the vignetting - i'm still feeling my way around the processing side of things).

I think what alacant was getting at is that it doesn't seem like the flats have been applied in the stacked image.

The fact that there is clear vignetting shows either the flats were not used during the stacking process or they are not correcting the image properly.

[Jonny_H]

7 hours ago, The Lazy Astronomer said:

I think what alacant was getting at is that it doesn't seem like the flats have been applied in the stacked image.

The fact that there is clear vignetting shows either the flats were not used during the stacking process or they are not correcting the image properly.

Ah apologies - I miss-understood.  I'm not really sure what I am doing wrong then when stacking! 😩 perhaps I will give DSS another go.

If I have added lights, darks, flats and bias frames for stacking, is there an obvious thing I should be checking as to why they are not correcting properly?

Thank you in advance for your patience!

[alacant]

11 hours ago, Jonny_H said:

lights, darks, flats and bias

Hi

Maybe post -links to- examples of each file type? That way we maybe able to pinpoint the problem.

Cheers

[Jonny_H]

9 minutes ago, alacant said:

Hi

Maybe post -links to- examples of each file type? That way we maybe able to pinpoint the problem.

Cheers

Thanks alacant,

I am thinking that the issue could be down to my flats being 'too White/bright'.  When I initially read up on them prior to my first session I think I missunderstood/misinterpreted the process 😳

Assuming this could be the main/sole cause?

[The Lazy Astronomer]

32 minutes ago, Jonny_H said:

Thanks alacant,

I am thinking that the issue could be down to my flats being 'too White/bright'.  When I initially read up on them prior to my first session I think I missunderstood/misinterpreted the process 😳

Assuming this could be the main/sole cause?

The histogram peak for flats should be about half way between the white and black points. If you think they're not good, you can go back and reshoot them if you haven't disturbed the imaging train (or changed focus position).

[Jonny_H]

10 minutes ago, The Lazy Astronomer said:

The histogram peak for flats should be about half way between the white and black points. If you think they're not good, you can go back and reshoot them if you haven't disturbed the imaging train (or changed focus position).

Unfortunately I packed the scope away yesterday otherwise I would have done! 

Oh well - lesson learned. Hopefully the next opportunity will prove to be more successful!

[The Lazy Astronomer]

2 hours ago, Jonny_H said:

Oh well - lesson learned. Hopefully the next opportunity will prove to be more successful!

We've all been there - my first attempt at flats were so bad they, if anything, introduced more dust motes. I find it helps if I think of astrophotography as one long, continuous string of mistakes which occasionally produces a passable image 🙃

 

[Jonny_H]

10 minutes ago, The Lazy Astronomer said:

We've all been there - my first attempt at flats were so bad they, if anything, introduced more dust motes. I find it helps if I think of astrophotography as one long, continuous string of mistakes which occasionally produces a passable image 🙃

 

😆