Halo or lenseeffect on stacked images

Currently I'm at work but in the afternoon I will upload it. Can you tell me where to upload it

Also please describe your image processing routine

So did you follow  this tutorial https://www.lightvortexastronomy.com/tutorial-pre-processing-calibrating-and-stacking-images-in-pixinsight.html to do the image calibration and registration?

Daniel:
No, I stack my pictures always with Deep Sky Stacker. Lights as Kappa Sigma and Darks as Median. Dark Optimisation is enabled. I don't use any Bias Frames. Just Lights, Darks, Flats and Flatdarks.

I suspect your flat subtraction could be responsible for the lighter image centre (I had a similar effect when the flats were too dark). A quick look at a few light subs will tell. Please upload a few light subs (FITS files) to one of those file sharing hosts and I will take a look.

Hi Daniel,

I looked at both light and dark frames and I think the problem is not with your optical train but with image calibration routine (bad dark optimisation or too dim flats).
The stretched light frame (a really nice sub), looks fine and does not show the halos you are getting in your processed images  - just a normal vignetting pattern:
https://www.dropbox.com/s/iu6uiudmdmhi3ft/M81_00001_d.jpg?dl=0

I suggest trying the following:
1) Disable dark optimisation, I had some strange results with it (similar to your halo)
2) Shoot brighter flats. Looking at your flat image I think it is too dim and may cause the halo when subtracted in DSS. The mean signal in the flat is 15000 ADU out of 65535 (max value in the light image). Ideally the flats should be between 50-75% of the max ADU (or ~40,000 ADU for your camera)
3) Try calibration in Pixinisight, it is superior to DSS: https://www.lightvortexastronomy.com/tutorial-pre-processing-calibrating-and-stacking-images-in-pixinsight.html

Cheers,
Alex

Try disabling dark optimisation and check if it helps to remove the halos.

Daniel:
Please tell me how you measured the ADU of the flat frame and what it's meaning?

in Pixinsight - Process -> Image statistics
Mean ADU shows the the average pixel value on the scale from 0 to 65535
For flats you want to be in a sweet spot of the detector - not too dark (otherwise you introduce extra noise) and not too bright (otherwise you will get artefacts arising from overexposure). A rule of thumb 50-75% of your max ADU

Hallo Tony
Ich habe bisher mit meiner EOS600 fotografiert. Da waren keine Bias notwendig. Daher habe ich bei der ASI294MC Pro auch (noch) keine Bias gemacht. Werde ich aber auch bei nächster Gelegenheit machen.
Danke und beste Grüße
Daniel