| 摘要 |
PURPOSE:To achieve display of a low magnification image without expansion and contraction or distortion of a sample image, by deflecting electron beams to be passed near the midway between the main face of an object lense and the front focus of it, in a low magnification image observation mode. CONSTITUTION:When a selection signal S which selects a low magnification image observation mode is applied to a mode switching gain control 7, gains of amplifiers 3a and 3b are controlled by the control 7 so as to change deflection ratio of deflection coils 2a and 2b and to deflect electron beams 1 to be passed near the midway between main face A of an objective lense and front focus B of it. Consequently, as an electron beam 1c is not passed through a cross point between the front focus B and an optical axis Z like an electron beam 1b is, an effect caused by spherical aberration is lessened and subsequently, extension of the electron beam scanning width or deformed scanning such as a barrel formed scanning on a sample are also lessened to a negligible degree. Thus, expansion and contraction or distortion of an image at displayed screen edges as shown by C in the figure may not happen.
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