The irradiation field is the size of the exposed surface of the X-ray beam incident on the limb; Controlled by line shielding with optical collimator, the size of irradiation field can be adjusted at will, which is convenient to use. In recent years, most X-ray machines produced at home and abroad are equipped with this equipment. There is also an automatic beam splitter with multi-blade structure, which has many functions. The size of the perspective irradiation field can be automatically limited to the visible area of the receiver (fluorescent screen or image intensifier) or the selected shielding plate, with automatic memory of the film size detector and film size specifications. The irradiation field of photography will be collimated according to the film size (or the selected shading plate), and it can automatically return to the previous perspective irradiation field after photography. When the distance between the focal point and the receiver changes, the blade opening will also change, keeping the set irradiation field size unchanged.