. Electron microscopy; proceedings of the Stockholm Conference, September, 1956. Electron microscopy. 100 W. D. RIECKE e G ft Fig. 2. Fine structures in tlie undift'racted beam in the diffrac- tion pattern from individual MgO crystals, (b) Pattern from the crystal shown in (a), and (d) that of the crystal (c). ( = 80 kV.) this lens was used to form an image of the diflFraction pattern, existing in the back focal plane of the objective lens, within the object plane of the projector lens, it had a focal length of cm and an astigmatic difference of focal lengths of cm. This limits th
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956. Electron microscopy. 100 W. D. RIECKE e G ft Fig. 2. Fine structures in tlie undift'racted beam in the diffrac- tion pattern from individual MgO crystals, (b) Pattern from the crystal shown in (a), and (d) that of the crystal (c). ( = 80 kV.) this lens was used to form an image of the diflFraction pattern, existing in the back focal plane of the objective lens, within the object plane of the projector lens, it had a focal length of cm and an astigmatic difference of focal lengths of cm. This limits the diffraction resolution to /? 1120 d, which shall be discussed in detail elsewhere, d is the diameter of the selected specimen area in /(. As to the resolution of fine structure in a reflection, the first-stage image of the scattering crystal practically acts as the aperture for the intermediate lens. The other rays, which pass the selecting aperture, do not contribute to this reflection. Even for a crystal size of I /*, an adequate resolution R ^ 1100 may be expected. Under these conditions, astigmatism and spherical aberration of the objective lens have no detrimental influence on the diffraction resolution. Apart from bright-held images or dark-field images taken with definite reflections, defocused diffraction patterns are useful for the interpretation of the focused ones (fig. 1, B, D). The overfocused dif- fraction pattern may be considered as a pin-hole projection of the second-stage image of the specimen onto the final screen. The "pin-holes" are formed by the reflections in the second stage image of the diffraction pattern (fig. 1, B)_ At this, the undiffracted beam produces a "bright-field" shadow image, and each reflection a corresponding "dark-field" shadow image. In a similar way, the underfocused diffrac- tion pattern may be regarded as a point-projection image of the second-stage image of the specimen. The projecting rays emanate fr
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