An optical element unit is provided comprising an optical element group for projecting light along an optical axis of the optical element group and a housing having an inner housing part partly defining a first space and a light passageway between the inner housing part and a second space. The inner housing part receives the optical element group. The optical element group comprises an ultimate optical element located in the region of the light passageway. A load-relieving device is provided adjacent to the ultimate optical element, the load relieving device partly defining the first space and the second space and at least partly relieving the ultimate optical element from loads resulting from pressure differences between the first space.