the invention relates to diaphragm means arranged close to the film in an x - ray spot film device . the diaphragm means comprises a first diaphragm with several rectangular aperture sections . the sections are displaced in the horizontal direction and have different vertical dimensions . a second diaphragm assembly has vertically extending diaphragm edges . by moving the first diaphragm to different positions in the radiation path , the aperture can be adapted to exposure formats of different vertical dimensions .