Apparatus for removing the scanning error due to an error in parallelism of a rotary polyhedral mirror

摘要

An improved method and apparatus for removing the scanning error due to imperfect parallelism of a rotary polyhedral mirror is disclosed. An incident beam of light initially deflected by the rotary polyhedral mirror is directed along an optical path which brings it back into incidence on the same deflection point on the mirror. The double deflection causes the second reflected beam to travel a path which is vertically independent of the error in parallelism, while at the same time not interfering with the horizontal scanning of the second reflected beam.