An antenna device for determining the filling level of a filling material in a container comprising an essentially flat array antenna with an emitting area for emitting measuring signals towards the surface of the filling material and a holder for holding the array antenna over an opening of the container and to be connected to the rim of the opening in at least two points of attachment. Such a multi-camera system typically includes a first image-capture device associated with a first optical train wherein the first image-capture device is typically pointed in a first direction. However, whilst this method is always workable, we have found that discolorations sometimes occur.