Method for capturing projection data by means of a computed tomography device, which has a radiation source for generating radiation, a detector and a collimator having a first diaphragm jaw and a second diaphragm jaw, the method comprising: - Positioning of the first diaphragm jaw and positioning of the second diaphragm jaw in such a manner that a layer collimation of a fan beam of the radiation is set by means of the first diaphragm jaw and of the second diaphragm jaw, - Capturing the projection data of a region of a patient to be imaged by means of the detector, while the detector and the radiation source are rotated in a plane of rotation about an axis of rotation and at the same time the region of the patient to be imaged is moved relative to the plane of rotation, wherein the fan beam penetrates the region of the patient to be imaged and strikes the detector, - Moving the first diaphragm jaw during the capturing of the projection data in such a way that a position (FG1, FG2) of a boundary surface of the fan beam is dynamically adjusted to a position (NG1, NG2) of a boundary surface of the region of the patient to be imaged, such that the fan beam penetrating the patient outside the region to be imaged is essentially avoided, - characterised in that the positioning of the first diaphragm jaw takes place in that a first rotational movement of a first threaded spindle is converted into a first translational movement of the first diaphragm jaw by means of a first threaded drive, and in that the movement of the first diaphragm jaw takes place in that a second rotational movement of the first threaded spindle is converted into a second translational movement of the first diaphragm jaw by means of the first threaded drive, - wherein the first rotational movement of the first threaded spindle and the second rotational movement of the first threaded spindle are driven by means of a first stepper motor, - wherein the second rotational movement of the first threaded spindle is controlled in a field-oriented manner. - Positioning of the first diaphragm jaw and positioning of the second diaphragm jaw in such a manner that a layer collimation of a fan beam of the radiation is set by means of the first diaphragm jaw and of the second diaphragm jaw, - Capturing the projection data of a region of a patient to be imaged by means of the detector, while the detector and the radiation source are rotated in a plane of rotation about an axis of rotation and at the same time the region of the patient to be imaged is moved relative to the plane of rotation, wherein the fan beam penetrates the region of the patient to be imaged and strikes the detector, - Moving the first diaphragm jaw during the capturing of the projection data in such a way that a position (FG1, FG2) of a boundary surface of the fan beam is dynamically adjusted to a position (NG1, NG2) of a boundary surface of the region of the patient to be imaged, such that the fan beam penetrating the patient outside the region to be imaged is essentially avoided, - characterised in that the positioning of the first diaphragm jaw takes place in that a first rotational movement of a first threaded spindle is converted into a first translational movement of the first diaphragm jaw by means of a first threaded drive, and in that the movement of the first diaphragm jaw takes place in that a second rotational movement of the first threaded spindle is converted into a second translational movement of the first diaphragm jaw by means of the first threaded drive, - wherein the first rotational movement of the first threaded spindle and the second rotational movement of the first threaded spindle are driven by means of a first stepper motor, - wherein the second rotational movement of the first threaded spindle is controlled in a field-oriented manner.