I use this to get aspect and arc working together.

CODE:
if (key_home == 1)
{
camera_arc += 0.1;
camera_aspect-= 0.001;
//
aCamera.arc = camera_arc;
aCamera.aspect = camera_aspect;
aCamera.arc = 1.5 * tan(aCamera.aspect);
if (camera_arc >= 130){ camera_arc = 130;}
if (camera_aspect <= 1){ camera_aspect = 1;}
//
}
//
if (key_end == 1)
{
camera_arc -= 0.1;
//OK now
camera_aspect+= 0.001;
//
aCamera.arc = camera_arc;
aCamera.aspect = camera_aspect;
aCamera.arc = 1.5 * tan(aCamera.aspect);
if (camera_arc <= 30){ camera_arc = 30;}
if (camera_aspect >= 2.0){ camera_aspect = 2.0;}
//
}