So you can't use Optitrack #MotionCapture cameras with #Vive Lighthouses because both use IR but the cameras can track your HMD. In theory. Unfortunately the software for configuring #SteamVR is outdated, it is not documented what it actually does and so I had to downgrade SteamVR, set the settings via said magical software and then upgrade SteamVR to current stable again because otherwise my #Unity project would not run anymore. And then you also can't easily change back to lighthouse tracking.