Removal or Hiding Dust Donuts

[admin]

Hi Dana,

Getting your flats right can indeed be tricky - there are a few variables/things to take into account.
I you haven't done so, have a look here.
Also, feel free to share your masterflat (or a single CR2/NEF/FITS frame) via Dropbox, Google Drive, OneDrive, WeTransfer, etc.
It may yield some clues.

Ivo