Calibration puzzle ...
 
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2022-05-29: APP 2.0.0-beta2 has been released !

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Calibration puzzle with bad flats


(@glennn)
Molecular Cloud Customer
Joined: 4 months ago
Posts: 7
Topic starter  

I have some very bad flats from a remote telescope. They have numerous dark rings in them, I assume this is dew? I only realized this when I processed the lights to completion. Regardless, the defective flats is not my puzzle, it's what I see in APP that baffles me.

I had 6 lights of each of LRGB. The first fully processed light (CA, STAR, REG, NORM) of each channel is always clear of the ring defects. Only lights 2 thru 6 show the rings. Why is the first free of defect? It almost appears that the flat correction was not applied to the first. the Have I discovered some bug in APP 1.083.3?

Attached is a PNG from one of the defective lights. I don't see those circles in the first image of each channel.

M83 Blue session 1 St

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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4856
 

These rings are dust on the sensor. They indeed require proper flats to be removed. Personally I've seen quite a few issues with online telescope services and calibration files, so that doesn't surprise me. It appears very hard to manage that properly, remotely. So, if you have these in your result, that means either that the flats are not applied to the lights, which can be due to a mismatch of calibration data vs lights. Or the flats themselves are not ok, not calibrated well, etc.

I would need to see what you used to be able to judge this better, so if you want to upload the data (the ones that fail), including the calibration data (masters are fine for now), that would be great.


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(@glennn)
Molecular Cloud Customer
Joined: 4 months ago
Posts: 7
Topic starter  

I created the upload folder as you suggested. In it are 4 files: (2) of original red light images, (1) Red MF generated by APP, and (1) Red "integrated" file.

The integrated file (isn't that the same as "stacked"?) actually doesn't look too bad, but the dust rings are obvious.

The master flats are full of dust rings. Should such flats be able to remove dust rings from the lights?

And why is it that the first fully processed light, pre-stack (CA, STAR, REG, NORM) appears to be free of dust rings, but all others are not?

 


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4856
 

Difficult to judge based in this data alone. But I am seeing a lot of dust on the masterflat you provided, so with that much it can become tricky for software to perfectly correct it. Also, there seems to be a lot of vignetting, I wonder if a flat that has been exposed longer would make better flats as well.


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