Patent ID: 6894834

Claim:
An objective having a first field plane, an intermediate image plane, and a second field plane, the objective comprising a first partial objective having a first, convex mirror with a first central mirror aperture and a second, concave mirror with a second central mirror aperture; and a second partial objective having a third, concave mirror with a third central mirror aperture and a fourth, concave mirror with a fourth central mirror aperture; wherein the first field plane and the intermediate image plane are conjugate planes relative to the first partial objective, and the intermediate image plane and the second field plane are conjugate planes relative to the second partial objective, wherein the first mirror has a first axial distance from the second mirror, the second mirror has a second axial distance from the intermediate image, and said first and second axial distances have a ratio between 0.95 and 1.05 relative to each other; wherein the third mirror has a third axial distance Z M3-IM from the second field plane, and said third axial distance conforms to the relationship 0.03 · Du M3 + 5.0 ⁢ ⁢ mm < Z M3 - IM < 0.25 · Du M3 tan ⁡ ( arcsin ⁡ ( NA ) ) , NA representing a numerical aperture NA in the second field plane, and Du M3 representing a diameter of the third mirror; and wherein further the second field plane has a fourth axial distance from the first field plane, and the objective has a Petzval radius whose absolute value is greater than said fourth axial distance.