SKEW THOUGHTS ON PARALLELISM

The non-parallelism introduced by the spiraling of electrons in the objective lens has greatly complicated the task of producing parallel illumination in the transmission electron microscope. This paper addresses the understanding and the techniques for minimizing the effects of the primary sources of non-parallelism: beam convergence/divergence (controlled by the excitation of the condenser lenses), the rotational divergence caused by the magnetic field in the objective lens and the angular spread introduced by the finite size of the electron source. The results are relevant to channeling and diffraction experiments and high resolution images.