LIGHT (OPTICAL) MICROSCOPY 



These are normally 35 mm cameias, with 

 their own eyepiece system built-in. Like the 

 trend toward built-in illumination, they rep- 

 resent the outcome of a demand for quick 

 convenient photography, resulting from the 

 permanently correct alignment built-in at 

 the factory. Focusing the picture is done 

 either via the binocular viewing system, or 

 by means of a small focusing viewer system. 



Coarse Adjustment. The ancient and 

 honorable rack and pinion persists as the 

 most popular means of coarse focusing. One 

 major difference in the modern microscope 

 is that many stands now focus the stage 

 rather than the body tube. The position of 

 the coarse adjustment has accordingly been 

 lowered to a more convenient height, per- 

 mitting operating it with the hand resting 

 on the table surface. In some stands the 

 coarse and fine focus controls are made con- 

 centric for greater ease, and rapidity of op- 

 eration. 



Fine Adjustment. Like the coarse ad- 

 justment, the fine adjustment is almost uni- 

 versally located in a low position permitting 

 use with the hand resting on the table sur- 

 face. On many stands it is now made con- 

 centric with the coarse adjustment. Unlike 

 the coarse adjustment, the fine adjustment 

 has undergone many changes through the 

 years, and no consistent design pattern exists 

 among various manufacturers. 



Most microscope makers have, however, 

 adopted ball bearings not only for the fo- 

 cusing slide, but for the thrust bearings on 

 the rotary control. Another trend, is to the 

 use of mechanisms, which permit using a 

 single focusing slide for both coarse and fine 

 focus, rather than the older style of a slide 

 carrying a slide. 



The basic mechanism which produces the 

 fine focusing motion is generally one of the 

 following: 



1 . Screw and nut with reducing lever. 



2. Screw and nut with reducing cam. 



3. Screw and nut with worm wheel. 



4. Cam and lever, friction clutch on pin- 

 ion. 



5. Planetary ball-bearing drive. 



6. Face cam with limits which engage 

 coarse adjustments. 



None of these has established a clear-cut 

 superiority over the others, and accordingly, 

 there seems to be no trend toward conform- 

 ity among microscope manufacturers in this 

 design feature. 



Stages. As has already been mentioned, 

 the stage in the modern microscope has been 

 made the focusable member, supplanting 

 the focusable body tube, and making feasible 

 the low position concentric coarse and fine 

 adjustment. 



Mechanical stages for accurately moving 

 and locating the specimen are supplied either 

 as accessory attachments or as built-in de- 

 vices. 



Li some cases both the 'east-west' and 

 'north-south' motion are accomplished by 

 sliding the specimen slide across the plain 

 stage surface. In others, this is true for only 

 one of these motions, the other being ac- 

 complished by moving the entire upper stage 

 surface. 



Another means of moving the specimen is 

 offered in the so-called 'GHde Stage', in 

 W'hich the entire upper stage surface is mov- 

 able by finger pressure in any direction. The 

 plate slides on a film of grease, and can be 

 moved with quite good precision as desired. 



Substages. The simplest substage equip- 

 ment, used on student microscope, consists 

 of a rotatable metal disc containing a num- 

 ber of different apertures, used to control 

 the N.A. of the illuminating beam. An iris 

 diaphragm supplants this disc in a slightly 

 better student model. 



Another simple form of substage contains 

 a 2-lens abbe condenser with iris diaphragm, 

 held either in a fixed focus mount, or a helical 

 focusing mount, in which focusing is done by 

 rotating the condenser. 



Once beyond the student level, however, 

 most microscope substages employ rack and 

 pinion focusing for the condenser. The con- 

 denser is normally clamped in a sleeve 

 mount, usually factory precentered. An iris 



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