Focusing device for focusing first beam in imaging plane

摘要

The focusing device (10) focuses a first beam in an imaging plane. The device has a first reflection surface (14) which deflects the first beam from a first direction into a second direction at 90 deg. to the first. The device has a second reflective surface (24) which deflects the first beam from the second direction into a third direction at 90 deg. to the second. The device also has a third reflective surface (26) which deflects the first beam from the third direction into a fourth direction at 90 deg. to the third. A fourth reflective surface (32) deflects the first beam from the fourth direction into a fifth direction at 90 deg. to the fourth. The second reflective surface (24) and the third reflective surface (26) are movable as a unit relative to the first reflective surface (14) and the fourth reflective surface (32).