Patent ID: 7697211

Claim:
An optical lens system for directing radiation from an object region to an image region, the optical lens system having an optical axis, the optical lens system comprising: a first lens group comprising first and second lenses positioned along the optical axis of the optical lens system; and a second lens group comprising first and second lenses positioned along the optical axis of the optical lens system, wherein: the first lens group has a first chromatic aberration for the radiation; the second lens group has a second chromatic aberration for the radiation; the radiation includes a wavelength, λ; a difference between a magnitude of the second chromatic aberration and a magnitude of the first chromatic aberration is less than about λ; the optical lens system images radiation at the wavelength λ to an image region; and a sign of the second chromatic aberration is opposite to a sign of the first chromatic aberration; and wherein the optical lens system forms a portion of a microlithography optical lens system and the first lens group reduces a curvature of the image at the wavelength λ in the image region to less than a depth of focus of the microlithography optical lens system in the image region of microlithography optical lens system.