DESIGN AND CONSTRUCTION OF THE LIGHT MICROSCOPE 



from the permanently correct alignment of a 

 built-in source of illumination (See Fig. 1). 



In some instances, instead of building the 

 source into the base, an attachable source is 

 made available which is interchangeable 

 with the mirror. Such sources are generally 

 of somewhat lower intensity than the built-in 

 sources, sufficient for most visual (bright- 

 field) tasks, but inadequate for photomicrog- 

 raphy, or special requirements, such as dark- 

 field or phase contrast. They are less expen- 

 sive than the built-in source and easier to 

 use than the mirror, since alignment is fixed. 



The built-in source, on the other hand, is 

 generally a very brilliant source, suitable 

 for photomicrography, darkfield, and phase. 

 A low wattage compact coil filament lamp 

 is employed using the traditional Koehler 

 illumination system, in which the lamp 

 condenser is imaged in the field, and the 

 coiled filament in the aperture of the system. 

 Filters and variable voltage taps on the 

 transformer provide means of controlling 

 the intensity of the illumination. 



The Arm. The traditional arm with in- 

 clination joint for tilting the microscope has 

 in large measure been supplanted by a rigid 

 non-tilting arm, which indeed is frequently 

 an integral part of the base casting. The arm 

 is normally hollow, enclosing the focusing 

 mechanisms. At its upper end, it is fre- 

 quently made in the form of a ring support 

 permitting mounting of interchangeable 

 microscope bodies, and rotation of the bodies 

 to any desired orientation. 



Bodies. Tilting the microscope on an 

 inclination joint has generally been sup- 

 planted by the use of inclined body tubes, 

 giving the same comfort of viewing, but 

 without the attendant undesirable tilting 

 of the stage. 



The trend is toward inclined binocular 

 bodies with their more natural fatigue-free 

 type of viewing. Some manufacturers supply 

 binocular bodies, which maintain a constant 

 tube-length despite changes in the inter- 

 pupillary setting. The advantage of this is 

 that it keeps the objectives working accur- 



FiG. 1 . This microscope depicts a good many of 

 the trends in the modern microscope, such as 

 built-in illumination, inclined binocular body, 

 built-in means for photography, and low position 

 coarse and fine adjustment. (Photo courtesy Ameri- 

 can Optical Co.) 



ately under nominal tubelength, and rigidly 

 maintains the factory setting for objective 

 parfocality. 



The so-called 'Triocular' body (Fig. 1) is 

 also becoming more popular. This is an in- 

 clined binocular with a third (vertical) eye- 

 piece tube for photomicrography. These con- 

 tain either a removable prism for directing 

 the light to either visual or photographic 

 systems, or a beam-divider, which directs a 

 portion of the light to each system. 



Built-in Cameras. Small built-in cam- 

 eras are finding increased favor over the 

 larger external photomicrographic cameras. 



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