microscope



microscope defined in 1951 year

microscope - microscope;
microscope - The ordinary microscope of the laboratory is a compound microscope with two sets of lenses (objective and eye-piece) which magnify the object in two steps. Biologists work with various magnifications, achieved by using objectives of different powers, commonly a 'low-power' or 'two-thirds' objective (giving a final magnification including that of the eye-piece of roughly 60-100 times), a 'high-power' or 'sixth' objective (final magnification of roughly 200-400 times) and an oil immersion 'twelfth' objective (final magnification 600-1000 times, sometimes up to 1,500 times). 'Two-thirds', 'sixth' and 'twelfth' indicate the focal length of the objective in inches. About 1,500 times is the maximum degree of magnification it is useful to have with ordinary light, because it is sufficient to make it easy to look at the finest detail that can possibly be seen ('resolved'). Further magnification reveals nothing more; the details merely look bigger and vaguer. This is because it is physically impossible with a microscope, however great its magnification, to see that two points are really two and not a single point when they are nearer together than approximately half the wavelength of the light used to illuminate them. Detail finer than this cannot be resolved. A modern compound microscope can almost reach this physical limit. Only by decreasing the wave-length of the illumination used can finer detail be resolved; and that is how the electron microscope achieves its immense power of detecting minute detail, the 'illumination' being by electrons, which have a very short wavelength.

near microscope in Knolik


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