An optical imaging system is to be aligned with its optical axis in relation to a given alignment axis. For this, a radiation beam is emitted from one side of the imaging system along the alignment axis. In the direction of beam propagation, there is located behind the imaging system a pair of diaphragm elements, whose apertures are each covered by a piece of material transparent to the radiation, carrying a plurality of sensor elements arranged in a matrix. The sensor elements furnish information about the measured radiation intensity to a signal processing unit, which can graphically illustrate the current alignment status of the imaging system on a monitor and/or produce an automatic adjustment of the imaging system.
