Method for limiting an X-ray beam, in particular in connection with an extraoral radiographic apparatus, wherein at least two blades (3, 4) of a blade limiting device (1) are moved through one common actuator (9) only, so as to produce an X-ray beam having the desired shape, wherein the actuator (9) moves the at least two blades (3, 4) at the same time, in a direct way and in the same direction, even in case of inversion of the direction of movement of said blades.