I dont know if it is normal or if something is wrong with my setup. Scratching my head as I did not have this with my previous setup (on previous setup I got normally looking flats, with brigher area in the center and darker area on the edges). So I'd appreciate any help...
Here are my 3 master flats for Ha, SII and OIII filters.
As you can see all 3 shows similar thing, bright edges and dark center.
This is my setup
Telescope: TS Optics Imaging Start 102mm APO with builtin flattener
Camera: QHY695A camera with OAG; Set of LRGB and NB Optolong filters 36mm unmounted
I create flats using USB controlled 520mm Artesky Flat Box
On my previous setup I did not had such problems, that setup had almost all the same stuff, but I changed telescope from Skywatcher 8'' newtonian to TeleskopService APO refractor, and also I changed from noname simple flatbox to that expensive one from Artesky.
And now I'm getting these results.
Do they look normal to you? Maybe its the way that APO with builtin flattener works? So maybe its expected?
Also, at this moment I cant really say if my flats correcting my lights fine, maybe you can see it from the stacked Ha image? The problem for me is that there is a lot of signal in this frame and I dont really know where it just background and where it is actual signal.
So what might be wrong here?