A problem about osgEarth::ViewPoint setFocalPoint

   I want to Follow more than 1 aircrafts viewpoint, When I use osgEarth::ViewPoint setFocalPoint to set the viewpoint in the center of aircratfs in event Handle. the viewpoint works normal,But there are 2 small problem:
   1,the mouse scroll don't work. the right mouse change range works normal.
   2,When I drag mouse,the viewpoint range become biger.
   How can I do to fix this?
   osgearth 3.0.