That's beautiful Christof! Very elegant and "minimalistic" design. I love the belt pulleys! Does the lens end up centered on the roll/tilt axes? How does it hold on to the round tube up top? Oh, and what's the weight?
One thing I'd like to see is a floating plate for the camera -- sitting on rubber standoffs, or something like that. To isolate the camera from as much vibration as possible. The isolation material might take some experimenting to get right... but I think it'd be worth it.
-Max