Electron microscopy; proceedings of the Electron microscopy; proceedings of the Stockholm Conference, September, 1956 electronmicrosco00euro Year: 1957 Strahlnchtung 1, Permanent magnet. 2a, 2b, Disploceable polepieces of the intermediate lens. 3, Insert, at the same time fixed pole- piece at the final projector lens. 4, Disploceable polepiece of the fmal projector lens. 5, Control nut. 6, Bevel gear. Fig. 1. Cross section through a two-stage projective system operating with permanent magnets. an electron microscope objective lens a permanent magnetic einzel-lens may be used. On its electron
Electron microscopy; proceedings of the Electron microscopy; proceedings of the Stockholm Conference, September, 1956 electronmicrosco00euro Year: 1957 Strahlnchtung 1, Permanent magnet. 2a, 2b, Disploceable polepieces of the intermediate lens. 3, Insert, at the same time fixed pole- piece at the final projector lens. 4, Disploceable polepiece of the fmal projector lens. 5, Control nut. 6, Bevel gear. Fig. 1. Cross section through a two-stage projective system operating with permanent magnets. an electron microscope objective lens a permanent magnetic einzel-lens may be used. On its electron optical properties Lenz (9) has published a paper. Such einzel-lenses and any lens system of two or more gaps operated by a single permanent magnet as described in a paper by v. Borries and Langner (4) show no image rotation, or, if the specimen im- merges in the field as is the case in strong lenses, the image rotation is at least small and does not vary noticeably when the magnification is changed. The size of such a system depends on the niagne- tomotoric force of the permanent magnet. The opti- mum shape of a permanent magnetic lens system has been calculated by v. Borries and Lenz (4), and it can roughly be said that for the diameter D of such a system, provided the best obtainable Alnico magnets with at least 10'' Gauss-Oersted are used, the following simple rule holds: Z) = 7 10 - mm Amp ' /, where / is the number of ampere-turns the magnet supplies when in the system. Based on the design of what we think an optimum system for an electron lens system with rotational symmetry three perma- nent magnetic electron microscopes have been com- pleted with / =i 2500 Amp on which papers have been published by v. Borries (1,2). Recently we have built a two-stage projector system of / = BOO^.. VergroOerung lC%%%%%%%%%%%%%%%% P loy. 5%%%%%%%%%%%%%%%% 10 75 —» ! mm ausgenulzler Bereich 20 Fig. 2. Magnification and distortion of a two-stage perma- nent magnetic projecto
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