Terrible purple vingette on flats

[drivera]

Hi there,

 

I completed flats this morning with my 533MC, GT71. I used Kstars to capture them with an ADU of 30000, and tolerance of 1k. I went to stack them and have a terrible purple vingette around the stacked file. I validated it was my flats when I stacked without them.

 

What causes this? Is it the light source or something else?  The image attached is stretched in Siril straight after stacking.

[GoldTop57]

Did you cool the camera when taking the flats? Was thinking there might be dew in the centre there.

[drivera]

29 minutes ago, GoldTop57 said:

Did you cool the camera when taking the flats? Was thinking there might be dew in the centre there.

Aah I wonder if that could have been it, as I did it after a night out shooting - brought it in and then about half-hour to hour later I did the flats. Will try again soon now its been inside and temps settled

[GoldTop57]

I had a very similar pattern in the centre with the ASI294MC Pro which I was able to eliminate by cooling to zero degrees in stages (or not bothering to cool at all). 

[drivera]

Awesome thank you! Seems like that might have been it. Just did the files again and they're fine, so came out okay! This is cropped but no vingette at all when I stacked them.

[Laurin Dave]

Possibly caused by one of the channels in the flat being saturated because of the colour of your light source.   to check I'd look at your master flat, debayer it, split the channels and measure the ADUs across the frame