In a method for three-dimensionally measuring a 3D aerial image in the region around an image plane during the imaging of a lithography mask, which is arranged in an object plane, a selectable imaging scale ratio in mutually perpendicular directions (x, y) is taken into account. For this purpose, an electromagnetic wavefront of imaging light is reconstructed after interaction thereof with the lithography mask. An influencing variable that corresponds to the imaging scale ratio is included. Finally, the 3D aerial image measured with the inclusion of the influencing variable is output. This results in a measuring method with which lithography masks that are optimized for being used with an anamorphic projection optical unit during projection exposure can also be measured.

In a method for three-dimensionally measuring a 3D aerial image in the region around an image plane during the imaging of a lithography mask, which is arranged in an object plane, a selectable imaging scale ratio in mutually perpendicular directions (x, y) is taken into account. For this purpose, an electromagnetic wavefront of imaging light is reconstructed after interaction thereof with the lithography mask. An influencing variable that corresponds to the imaging scale ratio is included. Finally, the 3D aerial image measured with the inclusion of the influencing variable is output. This results in a measuring method with which lithography masks that are optimized for being used with an anamorphic projection optical unit during projection exposure can also be measured.

A projection optical system capable of performing compact and proximate projection and a projector including the projection optical system. The projection optical system includes a first optical group which is a dioptric system and a second optical group which is a catoptric system. The second optical group includes a first catoptric system to a third catoptric system that have a first reflection surface with a concave surface shape, a second reflection surface with a curved surface shape, and a third reflection surface with a convex surface shape. The first catoptric system to the third catoptric system satisfy Conditional Expression (1) for focal distances. Image light emitted from the first optical group is reflected by the second optical group to be projected to a projection surface.

An imaging optical unit serves within a metrology system for examining a lithography mask. The lithography mask can be arranged in an object field of the imaging optical unit. The object field is defined by two mutually perpendicular object field coordinates. The imaging optical unit has an aperture stop of which the aspect ratio in the direction of the two object field coordinates differs from 1. This results in an imaging optical unit which can be used for the examination of lithography masks that are designed for projection exposure with an anamorphic projection optical unit.

In a method for three-dimensionally measuring a 3D aerial image in the region around an image plane during the imaging of a lithography mask, which is arranged in an object plane, a selectable imaging scale ratio in mutually perpendicular directions (x, y) is taken into account. For this purpose, an electromagnetic wavefront of imaging light is reconstructed after interaction thereof with the lithography mask. An influencing variable that corresponds to the imaging scale ratio is included. Finally, the 3D aerial image measured with the inclusion of the influencing variable is output. This results in a measuring method with which lithography masks that are optimized for being used with an anamorphic projection optical unit during projection exposure can also be measured.

An optical system includes a first optical element. The first optical element has a first transmission surface, a first reflecting surface arranged at a reduction side of the first transmission surface, and a second transmission surface arranged at the reduction side of the first reflecting surface. The first transmission surface has power. Light passing between the first transmission surface and the first reflecting surface includes peripheral light tilted in a direction of getting away from an enlargement-side conjugated plane as coming closer to the first transmission surface. The peripheral light is tilted in a direction of coming closer to the enlargement-side conjugated plane as getting away from the first transmission surface between the first transmission surface and the enlargement-side conjugated plane.