Abstract: A device for positioning a flattening filter in the center of an x-ray radiation, which comprises a drive means for driving the flattening filter between positions outside and inside the x-ray radiation; and a stop means for restricting the inside movement of the drive means to the center position of the flattening filter.

Abstract: The apparatus comprises a first apparatus part and a second apparatus part which is disposed on and extends outward from the first part. The second part is movable with respect to the first part between an attracted position, in which it is extended to a predetermined extent, and a retracted position, in which it is extended to a lesser extent. The apparatus also comprises a security device disposed on at least one of the first and second parts. This device includes a magnetic device for exercising an attractive magnetic force between the first and second parts. Thereby the second apparatus part is maintained in the attracted position. It also includes a spring device for exercising an attractive mechanical force between the first and second parts. The mechanical force is comparatively low in the attracted position. It increases with increasing deviation from the attracted position towards the retracted position.