Patent ID: 8664599

Claim:
An electron microscope comprising: an electron gun for generating an electron beam; a spherical aberration corrector; an objective lens; a specimen holder on which a specimen may be placed; a transfer lens system mounted between the spherical aberration corrector and the objective lens said transfer lens system is comprised of a pair of axisymmetric lenses for transferring the electron beam such that the principal plane of the final stage of the spherical aberration corrector is conjugate with the front focal plane of the objective lens and produces a magnification of 1 or more; an aperture stop placed in a stage preceding the spherical aberration corrector movably relative to an optical axis; and an angular aperture stop mounted at or near a principal plane of the transfer lens movably relative to the optical axis to adjust an angular aperture of an electron beam wherein said angular aperture stop is mounted between a principal plane of a rear one of the axisymmetric lenses and a front focal plane of the objective lens.