Backscatter removal in Darktable

[kofa (István Kovács)]

Could this be relevant? There, the issue was condensation on the lens, but maybe a similar approach could be used:

Diffuse module is now in the master.....

[PA111122_01] [PA111122] This is what I was able to get out of this photo with diffuse/sharpen. The lens was foggy (it was cold outside the conservatory).