Somebody @ dpreview attached the Ricoh DW-6 19mm Wide Conversion Lens to a Leica D-Lux 4 with a simple step down filter. The author claims that the tests photos were “sharp enough also at the extreme corner shooting in 16:9 format”. Here is a picture of the D-Lux 4 with the Ricoh DW-6:
Update (posted as a comment by a reader):
This brought me to an spontanous idea: i had already cut an old mountainbike-tube into slices for using the rubber rings i.e. for keeping cables rolled up. Why not using them to pimp up the 43 mm thread of the Ricoh converter, so that it sticks in the 45mm thread of the Lumix/Leica adapter? It takes two, and it fits. At last I pulled a third one (10 mm slice) around the outside and voila, everything is nice and secure in just 10 minutes time: