As I'm sure you can tell, the 3D renderer is quite limited compared to the 2D renderer. By default the camera is pointed at the centroid of all the node positions. However you can manually change this point...
- Go to the Style panel.
- Go to the Network tab.
- Click the "Properties" dropdown and select "Show All"
- You should now see properties for "Camera Center X/Y/Z".
- You can manually set these properties to position the camera center.
If you want to reset the camera to the center, go to the Layout menu and select "Center Network".
Hope that helps.