The electron microscope, its development, present performance and future possibilities electronmicrosco00gabo Year: 1948 76 The Electron Microscope tional features have probably remained unaltered in the commer- cial model which has just appeared on the market at the time of writing. A full view of the small microscope has been already shown in figure 17. Figure 23 is a slightly simplified section of it. The main dififerences from the large model will become evident from a comparison with figure 18. Starting from the cathode end, we note first of all the absence of the condenser lens. This h
The electron microscope, its development, present performance and future possibilities electronmicrosco00gabo Year: 1948 76 The Electron Microscope tional features have probably remained unaltered in the commer- cial model which has just appeared on the market at the time of writing. A full view of the small microscope has been already shown in figure 17. Figure 23 is a slightly simplified section of it. The main dififerences from the large model will become evident from a comparison with figure 18. Starting from the cathode end, we note first of all the absence of the condenser lens. This has been replaced by electrostatic focusing, by impressing different potentials on the cathode shield which in figure 23 is called the grid. If the grid is at cathode potential, the cross-over will very nearly coincide with the object which is now illuminated by a bundle of fairly wide divergence. This Inmdle is not cut off, as the new microscope contains no physical objective aperture. It contains only a small diaphragm between the electron source FLUORESCENT SCREEN PHOTOGRflPHID EMULSION PROJECTION LENS POLE PIECES OBJECTIVE LENS POLE PlECEb SPECIMEN STR6E SHIELDING flPERTURt GRID FILAMENT FILAMENT flOjUSTMENT INSULATING 6UN SUPPORT Fig. 23. Section of electron microscope, desk model
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