In a process for correcting pyramidal errors due to misinclination of facet surfaces of a rotating polygonal mirror (8) that receives light and is used to deflect a beam of light, wherein a misinclination of a facet surface prompts a corrective deflection of the light beam (5) reflected by the specific facet surface (12), at a correction angle opposite to the deflection by misinclination, the invention provides a continuous check on the orientation of the facet surfaces (16) as they pass a measuring point (15), a measure of the angle of misinclination when it occurs and an adjustment of twice the measure as angle of correction of the corrective deflection. A device for carrying out the process has a light-exposed rotating polygonal mirror (8) as well as a deflection device (9, 10) for corrective deflection of the light beam (5) in the event of a misinclination of facet surfaces and a control device which is used to drive the deflection device. With a measuring device (13) the orientation of each facet surface (16) can be continuously monitored with each pass of the measuring point (15), the angle of misinclination can be determined when it occurs and, as a function thereof, an input signal can be sent to the control device (36). |