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The Next Generation of TEMs

A selection of the more common questions arising during a typical lab course for materials majors learning to use a TEM is as follows 1) Why must I insert the objective aperture, which governs image contrast, in the diffraction plane? 2) Why must I insert the selected area diffraction aperture, which governs the diffraction pattern contrast in the image plane? 3) Why is the TEM relatively useless if both apertures are in at the same time or both are out? 4) Why is the contrast in my images always greatest when the beam is parallel - which makes the screen intensity so weak, I sometimes can't see the contrast anyhow? 5) Why, when I need to record a diffraction pattern, do I have to learn to estimate exposure time from the analog screen, rather than just push a button and get a correct exposure, as in most other optical instruments and cameras?