An optical element unit including a first optical element module and a sealing arrangement is disclosed. The first optical element module occupies a first module space and includes a first module component of a first component type and an associated second module component of a second component type. The first component type is optical elements and the second component type being different from the first component type. The sealing arrangement separates the first module space into a first space and a second space and substantially prevents, at least in a first direction, the intrusion of substances from one of the first space and the second space into the other one of the first space and the second space. The first module component at least partially contacts the first space and, at least in its area optically used, not contacting the second space. The second module component at least partially contacts the second space.