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Strange circular pattern in stacked images Other · Konrad Krebs · ... · 3 · 279 · 3

Konrad_Krebs 0.90
Konrad Krebs
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Hello everyone,

I took photos with two different telescopes on two different days in January. Now I have noticed that after stacking and calibrating, a strange circular pattern remains in both cases. The darks and flats look perfectly correct, I took the flats once with a t-shirt and once with a flatfield box. One of the images was taken with a Mak-Newton, the other with an APO. Camera was ZWO 294MC Pro, I photographed in the same observation location as usual, I have never experienced anything like this before. One night was new moon, the other about 50% moon. Temperatures were -3 to -9 degrees in both cases. I used heating strips. I will give example files for one of the nights.
Does anyone have any idea what the problem could be?

After stacking:
grafik.png

After ABE:
grafik.png

Link to raw files: https://www.dropbox.com/scl/fo/gxhnbgxpmt65ytdtmow3p/h?rlkey=ueetnncav0cmw77f1ptqvb8hk&dl=0
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AstroDan500 7.19
Dan Kearl
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I downloaded and looked at the images. I don't think your flat is correct . I have the 294mc and while your pattern looks bad, it looks like a fairly normal 294mc Uncalibrated image.
The Flat should show some of the pattern and it shows none.
I also have never seen a 294mc file without amp glow which doesn't show on your darks or on the stacked file.
Just my observations…
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Konrad_Krebs 0.90
Konrad Krebs
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Hi Dan,

I own this camera since 2,5 years now, and all my flats look like that. I never had such a pattern. My Darks of course show the AMP glow, maybe you looked into the Dark Flat?
Here the Dark:
grafik.png

If you stretch the flat a bit, you will also find the donuts of some dust spots, which are gone in the calibrated image. So my flats work I think. I take them with the ASI Air Plus in automated modus. So they should be right in terms of ADU.
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Semper_Iuvenis 3.10
Monty Chandler
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Reshoot your flats - 3 sec exposures - be sure to calibrate them with a master_dark_flat before creating your master_flat.   I assume you have a quality dark library to go with the flats in image_calibration and cosmetic correction.
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