| 摘要 |
PURPOSE:To obtain an optimum angular aperture on the back side focal surface of each of a high resolving power lens mode and an extremely low power lens mode by arranging a plurality of objective lens movable diaphragms in the upper and lower sides, along an optical axis, of each corresponding lens mode. CONSTITUTION:A sample 2 set in a sample holder 1 is fixed in an optical axis within an objective lens comprising an upper magnetic pole 3 and a lower magnetic pole 4. A movable diaphragm 6 having a plurality of stop holes 5 with different diameters is arranged in a lens space between the upper and lower magnetic poles. A movable diaphragm 9 having a plurality of stop holes 8 with different diameters is arranged in a through hole 7 installed in the lower magnetic pole 4. The back side focal surface in a high resolving power lens mode exists in the lens space, and an optimum angular aperture to obtain good contrast with small stop holes 5 is selected using the movable diaphragm 6. The back side focal surface in an extremely low power lens mode exists in the lower magnetic pole 4, and an optimum angular aperture to obtain good contrast with stop holes 8 is selected using te movable diaphragm 9. |
