Electron microscope having object limiting and contrast intensifying diaphragms

Claim 1

In an electron microscope comprising an electromagnetic objective lens including an energizing coil and having a given focal plane and a given image plane, a control lens and a projector lens, which lenses are arranged in order of succession along the axis of the microscope, a contrast-intensifying diaphragm and an object-limiting diaphragm successively arranged between the objective lens and the control lens, and a source of current for energizing the said objective lens energizing coil, the improvement comprising a variable impedance in series with said current source for adjusting the energizing current for said coil to a value for which the focal plane coincides substantially with the plane of the contrast-intensifying diaphragm and the image plane coincides substantially with the plane of the objectlimiting diaphragm, a fixed impedance in series with said variable impedance for supplying a current of fixed magnitude smaller than any current magnitude supplied by the variable means and for which the focal plane of the objective lens substantially coincides with the plane of the object-limiting diaphragm, and means to selectively connect said current source and said variable impedance without said fixed impedance in series with said objective lens energizing coil and to connect said lens in series with said variable and fixed impedance.