The use of optical microscope concentrators
①Reasons for using a condenser
When the magnification increases, on the one hand, because the higher the magnification, the higher the number of lenses, the more light is absorbed by the lens; on the other hand, because the brightness of the field of view (refers to the range of the specimen can be seen) and the magnification of the square is inversely proportional to the magnification of the magnification, that is, the higher the magnification, the darker the field of view. In order to get enough brightness, must be installed with a concentrator to focus the light on the specimen to be observed.
②Height at which the concentrator should be located during observation
When observing, to ensure the best observation effect, the focus of the concentrator should fall exactly on the specimen. To achieve this condition, it is necessary to adjust the height of the concentrator. When illuminated with parallel light, the focus of the concentrator is about 1.25mm above the centre of its upper lens plane, so it is often required to raise the concentrator to a height where its upper lens plane is only slightly below the plane of the carrier table when observing, so that the focus of the concentrator may fall on specimens located on slides of standard thickness. When using thinner than the standard thickness of the slide to bear the specimen, the position of the concentrator should be correspondingly lower, and when using too thick slides, the focus of the spotlight can only fall below the specimen, not conducive to fine observation.
③Concentrator and objective lens coordination
Here the so-called cooperation, is to make the concentrator and objective lens, the two values of the aperture to achieve consistency, in order to better carry out the more detailed observation. If the numerical aperture of the concentrator is lower than that of the objective lens, part of the numerical aperture of the objective lens will be wasted, thus failing to achieve its highest resolving power. If the concentrator's numerical aperture is greater than the numerical aperture of the objective lens, on the one hand, it can not improve the resolution of the provisions of the objective lens, on the other hand, the reverse will be due to the illumination beam is too wide, so that the clarity of the object image is reduced. Concentrator and objective lens with the operation method is: in the completion of the illumination, focusing operation, remove the eyepiece directly to the lens barrel, the concentrator under the variable diaphragm closed to the minimum, and then slowly open large. Open it until its aperture is exactly as large as the diameter of the field of view seen, and then press on the eyepiece to observe. Each time the objective lens is switched, it is necessary to carry out this co-ordination operation in turn. Some concentrator variable diaphragms have a scale engraved on the rim indicating the opening aperture, and can be fitted according to the scale.
Note: In the case of a teacher's microscope with an aperture diaphragm rather than an aperture, the best balance between maximum resolution and maximum contrast can be achieved by adjusting the numerical aperture of the aperture diaphragm (note that it is not the size of the physical diameter of the lens) to 80 per cent of the numerical aperture of the objective lens (see the labelling directly on the objective, e.g. a 10× objective lens may be 0.30, etc.).
