Why does vtkCamera auto adjust camera position after something rendered.

Hi all,
I tried to set vtkCamera to make the origin of world coordinate to be the middle of the render window.
It works if theres only a AxesActor display at the orgin. (actorAxes->SetPosition(0, 0, 0);
image

But when I tried to add another actor into renderer, the origin of world coordinate doesn’t display at the middle of the render window, camera fixed postion to fit the new actor I think.

image

How can I fix it please?