A physical part of an electron or ion microscope which holds the optical components of the device.

A single electron or ion microscope may have multiple columns.

It is possible to have optical components which are not contained in the column for example an EELS detector or an additional laser.

The column is a tube-like structure which allows propagation of the beam.

The exact definition of a column's boundaries may be ambiguous, for example a pole piece extending into the specimen chamber.