| http://www.w3.org/ns/prov#value | - It becomes necessary to change or vary the excitation of the objective lens, when the specimen position Zo is varied, as illustrated in FIGS. 2(a) and 2(c), due to tilting of the specimen or other causes, departing from the state in which the electron beam having been transmitted through the specimen disposed at the center 0 of the objective lens is focused to the predetermined point ZA (=d), as i
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