This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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An image plane is a plane in which the all paraxial rays originating from the center of the object plane join in a single point.

In selected area diffraction (SAD) technique in TEM, an aperture (called selected area aperture) is introduced into the image plane of the objective lens to select an area so that we can limit the region which generates the diffraction pattern. Note that the image plane of the objective lens is also the first image plane in the TEM system.

The caustic image in TEM is a disk with a bright spot. It is formed above the image plane when a convergent electron beam is focused at the object plane (sample plane) of the objective lens. The bright spot is the projection of the direct electron beam.