The invention relates to an X-ray device which includes a primary diaphragm device (3) for limiting the X-ray beam and a control circuit (10) for automatic exposure control, which control circuit includes a detector (9) with at least one measuring field (31) which measures the X-ray dose rate. Whereas in the case of customary exposure control systems the X-ray dose is increased when the radiation beam is strongly limited so that parts of the measuring field (31) are not exposed, which could lead to overexposed X-ray images, the X-ray device according to the invention is provided with means (12, 14, 15, 16, 17) for determining a correction value (K) which is dependent on the dimensions of the exposed area (33) of the measuring field (31) and acts on the control circuit (10) in such a manner that an increase of the X-ray dose is even avoided in the case of a partly non-exposed measuring field (31).

An X-ray examination apparatus includes a beam diaphragm (3) with an X-ray absorbing shutter (4, 31, 32) which is arranged between the X-ray source (1) and the X-ray detector (9) in order to intercept parts of the X-ray beam (2), thus forming a limited X-ray beam (7). The shutter (4, 31, 32) can be displaced according to different degrees of freedom by different rotations of control rings (21, 22, 41, 42, 47, 48) whereto the shutter (4, 31, 32) is coupled. Because the shutter (4, 31, 32) can be moved to practically any desired position within the X-ray beam (2), the beam diaphragm (3) can shape the cross-section of the limited X-ray beam (7) in such a manner that essentially only a part (5) of a patient (6) to be examined is exposed to X-rays.

An X-ray diaphragm which forms a pyramidal X-ray beam with use of a simple construction includes four blades which are arranged in a surrounding relation to four sides so as to form a pyramidal X-ray beam with an X-ray focus as a vertex, the four blades having a structure such that the blades are fitted in one another in the form of parallel crosses at portions corresponding to four-corner edges of the pyramid. The blades have respective plural cross beams, the cross beams being formed such that adjacent cross beams are fitted in each other. The distance between mutually opposed blades is variable.

With a view to providing a beam diaphragm having a large maximum value of aperture opening under a limited profile dimension, the beam diaphragm comprises a pair of control rings having coaxial apertures for the passage of X-rays therethrough and being opposed to each other axially through a spacing and coaxially rotatable independently of each other, a blade positioned between the pair of control rings, and position adjusting means which, in accordance with a relative rotation of the pair of control rings, causes the blade to move toward or away from a common axis of the apertures so as to describe a sectorial plane whose radius increases or decreases continuously.