The electron microscope, its development, The electron microscope, its development, present performance and future possibilities electronmicrosco00gabo Year: 1948 Commercial Electron Microscopes 77 Fig 24, Test photograph of simplified microscope. Thin membrane spattered with heavy metal. Electronic magnification X3,100 and the specimen, very near to the latter, in order to reduce the cross section of the beam and the heat development in the specimen. Such wide bundles produce large spherical aberration, and cannot be used for photographs with high resolution, but they are very usef
The electron microscope, its development, The electron microscope, its development, present performance and future possibilities electronmicrosco00gabo Year: 1948 Commercial Electron Microscopes 77 Fig 24, Test photograph of simplified microscope. Thin membrane spattered with heavy metal. Electronic magnification X3,100 and the specimen, very near to the latter, in order to reduce the cross section of the beam and the heat development in the specimen. Such wide bundles produce large spherical aberration, and cannot be used for photographs with high resolution, but they are very useful for focusing the specimen. Apart from the higher intensity, a wide bundle has the advantage of smaller depth of focus and enables more accurate focusing. When the picture is taken a potential of —73 volts is impressed on the grid, which not only cuts down the current, but brings the cross- over very close to the cathode and makes the illuminating beam at the specimen very nearly parallel, with a divergence near to the irreducible minimum, discussed in chapter 5. The specimen is no longer contained in a special object chamber with an air lock. The whole volume of the microscope is so small that a vacuum of the order of '^ mm mercury can be established in 1^-3 minutes, according to the length of
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Photo credit: © Bookworm / Alamy / Afripics
License: Licensed
Model Released: No
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