Orthogonal magnetic quadrupole lens systems that could serve as electron microscope objectives are treated theoretically. After certain constraints are placed on the quadrupole field strength, the calculus of variations is applied to obtain systems with minimum chromatic aberrations. A digital computer was used to calculate optimum orthomorphic and anamorphotic objective type systems. The resulting orthomorphic systems have four lenses while the corresponding anamorphotic systems have three. The chromatic aberration only varies by a factor of 2 in this study indicating its relative insensitivity to choice of lens systems. It is found that the optimum quadrupoles have about 3.6 times as much chromatic aberration as round lenses with comparable fields and dimensions.

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© 1971 The American Institute of Physics.
1971
The American Institute of Physics
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