Hi Janek
Sorry I dont know what you mean by an “extension ring” do you mean extension tube?
You seemed to have nailed the focus stack - with the subject nice and crisp/sharp
The background looks a bit strange in how it interacts with the subject. There is a clear demarcation of a lighter area of background that looks strange.
Maybe you can select the subject as a mask - and then darken and blur the background so the subject “pops” out of the frame nicely.
Fantastic effort on your first focus-stack
regards
Huw
