| 摘要 |
PURPOSE:To prevent movement of a visual field and change in the visual field radius of a diffraction pattern when a convergent angle is changed by changing the excitation intensities of the 1st and 2nd convergent lenses and auxiliary lens cooperatively with the change in the excitation intensity of an objective lens. CONSTITUTION:An operator changes the front magnetic field lens 4a of an objective lens by adjusting an adjuster 12 so as to make the diffraction spot of the diffraction pattern on a fluorescent plate as large as possible within the range when the spots do not overlap each other while observing said spots. Control signals are supplied from converters 13, 14 to excitation power sources 9, 10 by which the excitation intensities of the 1st and 2nd convergent lenses 2, 3 are so excited that the image of an electron tun 1 is formed successively at the same magnification on a sample 5. The position and magnification of a rear magnetic field lens 4b change as well as a change in the output from the adjuster 12 but an auxiliary lens 15 crosses over the diffracted electron rays around a cylindrical part 6 in succession by a converter 17 and an excitation power source 16 and therefore the visual field radius of the diffraction pattern image is maintained max. |
