Patent ID: 8345350

Claim:
An objective comprising: a plurality of optical elements arranged to image a pattern from an object field in an object surface of the objective to an image field in an image surface region of the objective at an image-side numerical aperture NA>0.8 with electromagnetic radiation from a wavelength band around a wavelength λ, the optical elements including a number N of dioptric optical elements, each dioptric optical element i made from a transparent material having a normalized optical dispersion Δ n i =n i (λ 0 )− n i (λ 0 +1 pm) for a wavelength variation of 1 pm from a wavelength λ 0 , wherein the objective satisfies:  ∑ i = 1 N ⁢ Δ ⁢ ⁢ n i ⁡ ( s i - d i )  λ 0 ⁢ NA 4 ≤ A for any ray of an axial ray bundle originating from a field point on an optical axis in the object field; where s i is a geometrical path length of a ray in an ith dioptric optical element having axial thickness d i and the sum ∑ i = 1 N ⁢ Δ ⁢ ⁢ n i ⁡ ( s i - d i ) extends on all dioptric optical elements of the objective, and where A= 0.2.