. Laboratory work in bacteriology. Bacteriology. THE MICROSCOPE. 133 It is well to have three eye-pieces, having an equivalent focal distance of 50, 35 and 25 mm. respectively. This cor- responds to numbers 0, 2 and 4 of Leitz, and 2, li and 1 inch eye-pieces of this country. As a rule, the low eye- piece should be used for work. â The higher eye-pieces may be used, when it is desired to increase the magnification. It should be remembered, however, that the eye-piece magni- fies the image, and hence, any imperfections that may exist in the image. On account of eye-piece magnification, the fiel
. Laboratory work in bacteriology. Bacteriology. THE MICROSCOPE. 133 It is well to have three eye-pieces, having an equivalent focal distance of 50, 35 and 25 mm. respectively. This cor- responds to numbers 0, 2 and 4 of Leitz, and 2, li and 1 inch eye-pieces of this country. As a rule, the low eye- piece should be used for work. â The higher eye-pieces may be used, when it is desired to increase the magnification. It should be remembered, however, that the eye-piece magni- fies the image, and hence, any imperfections that may exist in the image. On account of eye-piece magnification, the field becomes darker and less distinct. It is preferable, therefore, to obtain an increased magnification by changing the objectives, rather than by the use of deep oculars. When apochromatic objectives, are used, it is possible to employ even the deepest compensation oculars. The Abhe condenser.âThis is a most important accessory to a microscope, and, indeed, it should not be wanting on an instrument intended for bac- teriological work. The usual Abbe condenser is chromatic, although for special purposes, as in micro-photography, an achro- matic condenser is employed. The ordinary condenser is made of two lenses, as shown in Fig. 19, and has a numerical aperture of By the introduction of a third lens, the aperture is in- creased to The aim of the condenser is to illuminate the object as much as possible. Without a condenser, given a plane mirror, an object will be illuminated by a pencil of light corresponding to its own diameter. This may be sufficient for a low power, but when high powers are used, it is evident that more light must be thrown on the object in order to see distinctly. By means of the condenser, the. Fig. 19. Cross-section of the Abbe condenser, showing convergence of the rays of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illus
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