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Electron lenses are the magnetic equivalent of the glass lenses in an optical
microscope and to a large extent, we can draw comparisons
between the two. For example the behaviour of all
the lenses in a TEM can be approximated to the action
of a convex (converging) glass lens on monochromatic
light. The lens is basically used to do two things
- either take all the rays emanating from a point
in an object and recreate a point in an image,
- or focus parallel rays to a point in the focal
plane of the lens.
 In
a TEM can we expect to have 'monochromatic' radiation
passing through every lens?
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