The IMX294 chip can suffer from a problem in which the red channel in particular, and sometimes the green as well, suffer "swirls", particularly around the perimeter of the frame. The exact cause of this is still debated, but it is definitely associated with flat calibration. Here is a thread with a good example:
https://www.cloudynights.com/topic/8290 ... ry11977169
The swirl is not seen without flat calibration, but then of course without flat calibration dust shadows and vignetting are not corrected.
In that thread I came up with a solution to the problem, which was then modified a bit by another poster because sometimes the artifact shows up in the green channel as well as the red, but never the blue. The solution is to create a master flat as normal, but then debayer it, and only use the blue channel for flat calibration of the lights. I figure that this should be pretty straightforward to implement and can be turned on with a setting in the SharpCap settings, such as "Use Blue Channel Only For Flats."
Here is an example from that thread showing the problem after standard flat calibration:
![Image](https://www.cloudynights.com/uploads/gallery/album_19272/gallery_390121_19272_6728120.jpg)
And here is a calibrated light from another user who implemented the blue-channel-only flat fix:
![Image](https://www.cloudynights.com/uploads/monthly_06_2022/post-160007-0-63633100-1656183115.jpg)
As you can see, the artifact is completely eliminated.
This may be relevant to other cameras than IMX294 based ones, but that is the one where I see this problem come up over and over and over.
Thanks for your consideration.