Patent ID: 6605810
Filing Date: 2003-08-12
Classification: H01J

Abstract:
An apparatus for correcting a third-order spherical aberration in a lens, comprising:an objective lens; a correction device positioned in a downstream direction of a propagation of optical rays, said correction device comprising a first hexapole and a second hexapole with a round-lens doublet being arranged between said first hexapole and said second hexapole, said round-lens doublet comprising a first round lens and a second round lens of equal focal lengths, with said first round lens and said second round lens positioned with a distance between one another equal to two focal lengths of said equal focal lengths, said first round lens being a distance of one said focal length from said first hexapole and said second round lens being a distance of one said focal, length from said second hexapole; and, an additional single round-lens positioned between said objective lens and said corrective device, so that a parallel downstream path of optical rays strikes said correction device with an aberration-free plane of said objective lens being represented on an aberration-free plane of said first hexapole of said correction device.