WPF, 3d camera won't rotate correctly

WPF, 3d camera won't rotate correctly

I'm trying to make my camera rotatable around the center point by holding
down the left button. Here's my code so far:
private void mouseWheel(object sender, MouseWheelEventArgs e)
{
if (e.Delta < 0) { _posZ = _posZ - 0.5; } else { _posZ = _posZ +
0.5; }
_perspectiveCamera.Position = new Point3D(_posX, _posY, _posZ);
}
private void mouseMove(object sender, MouseEventArgs e)
{
if ( e.LeftButton == MouseButtonState.Pressed )
{
if (isLeftDown == false)
{
isLeftDown = true;
tempMouseX = this.PointToScreen(Mouse.GetPosition(this)).X;
tempMouseY = this.PointToScreen(Mouse.GetPosition(this)).Y;
}
else
{
double currentDelataX = tempMouseX -
this.PointToScreen(Mouse.GetPosition(this)).X ;
double currentDelataY = tempMouseY -
this.PointToScreen(Mouse.GetPosition(this)).Y ;
_posX = _posX - currentDelataX / 1000;
_posY = _posY - currentDelataY / 1000;
_perspectiveCamera.Position = new Point3D(_posX, _posY,
_posZ);
Point3D objectPosition = new Point3D(0, 0, 0);
_perspectiveCamera.LookDirection = new
Vector3D(objectPosition.X - _perspectiveCamera.Position.X,
objectPosition.Y - _perspectiveCamera.Position.Y,
objectPosition.Z - _perspectiveCamera.Position.Z);
}
}
/////////////////////////////////////////
if (e.LeftButton == MouseButtonState.Released)
{
isLeftDown = false;
}
}
Yet the rotation itself doesn't seem to work right, looks like the camera
moves far away by the Z axe ( object moves away from the viewer ).
What do you think might be wrong?
Thanks