Dust Subtraction

[brenski]

This is DSS stack of C2022 E3 ZTF. I've cropped the image down to show the dust elements. I've left a tiny section of the comet in (which was centre frame) to help illustrate how imposing these "specs" are. Don't know if anyone has a solution to this, but my darks, flats and bias frames appear to have had no effect. Equipment: Zwo ASI183MC Pro (cooled), Evostar 72 ED DS Pro, S/Adv 2i.

[Menno555]

I've had these dust specs also. They're very big and faint and would not disappear.
My reasoning was that I did make my flats (I manke them manually) with my standard settings, meaning around 25000 ADU, but maybe this was too bright and the light from my flatpanel was just "shining through" these parts?
So I made flats at a lower ADU (15000 if I remember correctly) and that indeed helped. So maybe try that and see if it helps?

Tip: maybe you already have it but a photographic air bellow did wonders for me. One of my best and cheapest astro purchase ever

Menno

[brenski]

I've had these dust specs also. They're very big and faint and would not disappear.
So I made flats at a lower ADU (15000 if I remember correctly) and that indeed helped. So maybe try that and see if it helps?

Tip: maybe you already have it but a photographic air bellow did wonders for me. One of my best and cheapest astro purchase ever

Menno

thanks Menno.
My flats are taken at same Exposure and Gain as my Lights.

I use the bellow before each session.
My understanding is that the dust can be in one of three places:
♦ ASI Camera - sensor protective Glass cover
♦ Scope Lens - inside
♦ Scope lens - outside.

Had so many battles with this Astro adventure, feel like it's just one more battle after the last.

[Menno555]

Flats typically are made with all the same settings as your lights except for exposure times. Only darks are needing the exact same settings as your lights.
Depending on your filters used, flats are generally short in exposure times. My flats are in general between 2sec to 8sec.
To come to this I play around with both my flat panel brightness and exposure times until I get around 25000 ADU (or when you are using the white T-shirt methode, add or remove fabric layers).
To see the ADU value, you have to open the Histogram. In the screenshot below I circled the ADU value in green on the right. Did search a little bit and I did see that other people with that same camera are using around 20000 ADU.

About the dust: it can be on anything that is in your image train. Dust on your scope lens can do no harm, that will not give any troubles in general. But it can never do any harm to blow it away of course.
But dust on your filters, protective glass, corrector/flattener, barlow, and so on, will.
And here a general rule when it comes to dust: the sharper and smaller the particle appears, the closer it is to your camera sensor.
So in this case the dust is faint and big, meaning it far away from your sensor. So somewhere at the beginning of your image train. When the dust specs are showing small and sharp, they are most likely on the protective window.

And yes, it can be a kind of battle to understand it all and get it right. When I was learning about calibrations files, I was getting frustrated because it looked like each thing I changed, affected another thing. Until I understood the balance of it all.

Hope this helps a bit.
Menno

ADU flats.jpg (292.06 KiB) Viewed 1415 times

[brenski]

thanks Menno

I'll do some new Flats - see how things turn out.

Regarding dust in the image train, with it being that "fuzzy" is it fair to say it's (likely) on the reducer/flattener or LP Filter?

[jolo]

If that is really a dust donut you may calculate the distance of the dust from the sensor using for example this calculator

http://www.wilmslowastro.com/software/formulae.htm#Dust

[Menno555]

thanks Menno

I'll do some new Flats - see how things turn out.

Regarding dust in the image train, with it being that "fuzzy" is it fair to say it's (likely) on the reducer/flattener or LP Filter?

Yes, that is correct.

If that is really a dust donut you may calculate the distance of the dust from the sensor using for example this calculator

http://www.wilmslowastro.com/software/formulae.htm#Dust

Thanks for that link, didn't know that one yet. Indeed some useful things there.

Menno