Patent ID: 7378667

Claim:
A particle-optical appliance provided with an objective lens and with aberration-correcting means for correcting lens errors of the objective lens, which aberration-correcting means comprise: a first group of optical elements, consecutively consisting of a first, a second and a third quadrupole lens and a first octupole; a second group of optical elements, consecutively consisting of a second octupole and a fourth, a fifth and a sixth quadrupole lens; and at least one third octupole, placed outside both groups of optical elements, whereby the first and the second octupole and the third and the fourth quadrupole lens are placed between the first and the second quadrupole on the one hand and the fifth and the sixth quadrupole on the other hand, in which the quadrupole lenses determine the paths of electrically charged particles in the aberration-correcting means in such a manner as to cause imaging of octupoles upon one another, characterized in that in a first axial plane, the first and the second octupole are not imaged upon one another, and the second and the third octupole are imaged upon one another; in a second axial plane perpendicular to the first axial plane, the first and the second octupole are not imaged upon one another, and the first and the third octupole are imaged upon one another; and an axial beam in the first axial plane passes through the axial point of the first octupole and in the second axial plane passes through the axial point of the second octupole, as a result of which third-order lens errors are corrected, and fifth-order lens errors are, at the least, minimized.