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INDI Library v1.9.8 Released (29 Sep 2022)

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Strange artefacts on my images

  • Posts: 24
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Dear all,

I am using a Skywatcher 420 t2ED scope for my imaging. The chain from the scope to the camera is like this:

Skywatcher AP 72/420 Evostar
—> Skywatcher Reducer/Flattener 0,85x
—> TSVF208 = 8mm
—> TSM54a-M48i = 1.5mm
—> Pegasus Falcon Rotator = 18mm
—> M48Abstimm05/Ring = 0.5mm
—> M54a-M48a (Pegasus adapter) = 2mm
—> Filterdrawer TSFSLM48 = 18mm
—> M48i-M48i = 0mm
—> ASToptics Adapter M48 Male to M42 Female - (5MM) = 0mm
—> ASI 183 = 6.5mm

It is not exactly 55mm, but very close (54,5mm).

When I take flat frames, I end up with images as the attached one. Unfortunately, the circles are also pretty much present in the final images when I processed them with Pixinsight. I cleaned all devices (whereever I could reach them) properly. This didn't change anything. I pulled out the single components one after the other (my first idea was the filterdrawer, but that didn't change anything) and the problem is still present.

Does anyone have an idea what is causing this?

Kind Regards

Ralf.
3 months 5 hours ago #85938
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Hi Ralf,

A real back of the envelope calculation
astronomy.tools/calculators/dust_reflection_calculator

Plugging in 72mm, 420mmFL, 0.85FR, 2.4umPIX and 687 pixels donut size I get approx 8mm.
Best guess is the sealing glass cover on the front of the CCD camera itself

Gene
The following user(s) said Thank You: Ralf Karpa
3 months 4 hours ago #85940

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Thank you Gene! I didn‘t even know that such tool for calculation exists. I will check out with my image again.

I will check the camera again for any dust.
2 months 4 weeks ago #85946

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That was the solution. I found several dust spots on the camera's glass. Got rid of them and the artefacts are gone! Thanks again!
2 months 4 weeks ago #85982

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If you use flat frames as part of your image calibration process, these dust bunnies should disappear. If they don't, there is something wrong with the image calibration process.
If you don't use flat frames, imo, you really should start using them.
Wim

Skywatcher 190MN + 150PDS, AZ-EQ6 GT + EQ3-2 Goto, ZWO ASI294MM Pro + ZWO ASI174MM-Cool, Raspberry Pi4 with Astroberry + Rock64 x 2 with INDI & PHD2

www.astrobin.com/users/wimvb/
2 months 4 weeks ago #85983

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Ralf,

I think these look like perfectly normal flats. I had very similar few dots in my flats for years. Don't worry about it.
2 months 4 weeks ago #85987

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