Som Berthiot Pan-Cinor 30 DV (10-30mm f/2.8)
The thread on the back of the lens can be rotated with a coin, allowing easy shooting in portrait or landscape orientation.
Without rotating the thread, by default, the viewfinder sits on the left side of the lens when held horizontally. However, the viewfinder does not clear the left side of the Q body, so you get a diagonal image in the viewfinder.
The only (minor) problem with this is that your image in the viewfinder is vertical when shooting horizontally.
For the street shots, I have used the orientation on the right.