12. More Detail: Size of a viewport can be changed.
By default, the viewport of a camera is the same size as the game window.
The size of a camera viewport can be changed.
Even the viewport of the active camera. It doesn't have to be full screen.
If you create a viewport 1/2 the size of the game window, it does not show the whole camera view at 1/2 the size. It shows 1/2 of the camera view at full size. From the center.