Hi Petra
I am running an SW Black Diamond ED102, with the SW 0.85 reducer/flattener and a Canon 60da. I havnt needed any extension tubes though. With this reducer you would need the wide version of the EOS tRing as its an M48 thread. Bintel have those.
This is the reducer/flattener. Cant see it on the bintel site though thats were I got it from
http://www.skywatcher.com/product.php?cat=28&id=179
Imaging train in photo attached
You do get a very flat image with this combo. Was quite impressed.
Hope this helps