Patent ID: 7989776

Claim:
A corrective for eliminating a third order aperture aberration and a first order, first-degree axial chromatic aberration, the corrective comprising: a first correction piece having an odd number of at least five multipole elements for generating quadrupole fields and at least one octupole field, said first correction piece being symmetrically constructed about a central plane thereof, with a central multipole element for generating a quadrupole field of said first correction piece being centered relative to said central plane of said first correction piece and having combined electric-magnetic quadrupole fields; a second correction piece having an odd number of at least five multipole elements for generating quadrupole fields and at least one octupole field, said second correction piece being symmetrically constructed about central plane thereof, with a central multipole element for generating a quadrupole field of said second correction piece being centered relative to said central plane of said second correction piece and having combined electric-magnetic quadrupole fields, said second correction piece being arranged behind said first correction piece in a direction of an optical axis, wherein said quadrupole fields in said second correction piece are oriented antisymmetrically to those in said first correction piece, said quadrupole fields being set such that an intermediate image lies substantially in a first quadrupole field and a last quadrupole field of said first correction piece and of said second correction piece; a transfer lens system arranged symmetrically relative to a central plane of said corrective, said transfer lens system including at least one round lens, a setting of said transfer lens system taking place so that said central plane of said first correction piece and said central plane of said second correction piece are imaged anamorphically on one another, wherein a magnification in a first principal section is a reciprocal of a magnification in a second principal section, said central quadrupole field of said first correction piece and said central quadrupole field of said second correction piece being superimposed by an octupole field.