Piece of Orion

Here is a photo taken with Pentax K-1 and SMC Pentax-F 1:4.5 300m * lens.

It is stacked from 28 300s exposures at ISO 100. Of course the session was driven by AstroBox M4 :-) I was stacking the photos using SIRIL and then made some adjustments in Darktable. The biggest and still not solved problem is how to get rid of this huge gradient...