An optical projection system (2, 1002, 1102) for a microlithography system comprising - a light path, - a first optical sub-system (7, 1007) receiving a first part of said light path, - a second optical sub-system (8, 1008) receiving a second part of said light path, and - a support unit (3, 1003) supporting said first optical sub-system (7, 1007) and said second optical sub-system (8, 1008); - said support unit (3, 1003) comprising a housing (3.1, 1003.1) receiving a third part of said light path; - said housing (3.1, 1003.1) comprising at least a first interface (3.4, 1003.2) and a second interface (3.4, 1003.4); - said first interface (3.4, 1003.2) being a first support interface (3.4, 1003.2) supporting said first optical sub-system (7, 1007); - said second interface (3.4, 1003.4) being a second support interface (3.4, 1003.4) supporting said second optical sub-system (8, 1008); - said first optical sub-system (7, 1007) and said second optical sub-system (8, 1008) being elongated units comprising a plurality of optical elements (7.2, 8.2, 1007.2, 1008.2); - said housing (3.1, 1003.1) receiving a further optical sub-system (10, 1010) of said microlithography system, said further optical sub-system (10, 1010) comprising two reflective elements (10.1, 10.2, 1010.1, 1010.2) mounted to said housing (3.1, 1003.1); - said housing (3.1, 1003.1) having a central first housing axis (3.2) and an outer wall (3.3, 1003.3) extending in a circumferential direction about said first housing axis (3.2); - said outer wall (3.3, 1003.3) being at least one of substantially symmetric with respect to said first housing axis (3.2) and substantially rotationally symmetric with respect to said first housing axis (3.2); characterized in that, - in said light path, no further optical element is located between said two reflective elements (10.1, 10.2, 1010.1, 1010.2). - a light path, - a first optical sub-system (7, 1007) receiving a first part of said light path, - a second optical sub-system (8, 1008) receiving a second part of said light path, and - a support unit (3, 1003) supporting said first optical sub-system (7, 1007) and said second optical sub-system (8, 1008); - said support unit (3, 1003) comprising a housing (3.1, 1003.1) receiving a third part of said light path; - said housing (3.1, 1003.1) comprising at least a first interface (3.4, 1003.2) and a second interface (3.4, 1003.4); - said first interface (3.4, 1003.2) being a first support interface (3.4, 1003.2) supporting said first optical sub-system (7, 1007); - said second interface (3.4, 1003.4) being a second support interface (3.4, 1003.4) supporting said second optical sub-system (8, 1008); - said first optical sub-system (7, 1007) and said second optical sub-system (8, 1008) being elongated units comprising a plurality of optical elements (7.2, 8.2, 1007.2, 1008.2); - said housing (3.1, 1003.1) receiving a further optical sub-system (10, 1010) of said microlithography system, said further optical sub-system (10, 1010) comprising two reflective elements (10.1, 10.2, 1010.1, 1010.2) mounted to said housing (3.1, 1003.1); - said housing (3.1, 1003.1) having a central first housing axis (3.2) and an outer wall (3.3, 1003.3) extending in a circumferential direction about said first housing axis (3.2); - said outer wall (3.3, 1003.3) being at least one of substantially symmetric with respect to said first housing axis (3.2) and substantially rotationally symmetric with respect to said first housing axis (3.2); characterized in that, - in said light path, no further optical element is located between said two reflective elements (10.1, 10.2, 1010.1, 1010.2).