Traditional Culture Encyclopedia - Photography and portraiture - Why does the "box" in the viewfinder move when the paraxial camera focuses? Is this the case with Leica M9?

Why does the "box" in the viewfinder move when the paraxial camera focuses? Is this the case with Leica M9?

The concept of paraxial is that the optical path of viewfinder and the optical path of shooting are not on the same axis.

In order to obtain the same observation range as the shot image, it is necessary to adjust the observation frame at different focal lengths. This is a new technology after the development of electronic technology. On traditional cameras, the photographer estimates the change of shooting range by himself.