Title: Long focal length magnetic lens for the optical imaging of a specimen having a large surface area

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Abstract: An improved magnetic lens having a long focal length for the optical imaging of a specimen having a large surface area by means of a charged-particle beam. The lens includes a cylindrical coil including at least one winding which is surrounded by a field-carrying metallic shell member fabricated of magnetic material disposed at the radially outer surface of winding. The improvement of the invention comprises a first ring member disposed on the radially outer surface of the metallic shell member approximately in the plane of the center of gravity of the lens; a plurality of slidable shoe members disposed on a lower surface of the first ring member; a housing fabricated of magnetic material surrounding the lens and including an annular shoulder on the radially inner surface thereof; a second ring member fabricated of non-magnetic material disposed on the annular shoulder for supporting the slidable shoe members, the shoe members being disposed between the first and second ring members; and at least three adjusting pin members distributed approximately uniformly over the surface of the housing and fabricated of non-magnetic material. The pin members extend through the housing and engage the first ring member of the metallic shell member for adjusting the position of the lens in a direction perpendicular to the axis of the lens.


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