The Use of the Microscope 35 



Centering the Field Condenser 



1. Open the substage iris and rack the condenser up to the top of its 

 travel. Leave the XlO ocular in position. 



2. Close the field iris (the lever seen in the dark slot just in front of 

 the microscope on the Ortho-Illuminator) and use the coarse adjustment 

 of the microscope to focus an image of the field iris. Make sure that you 

 are actually looking at this iris by opening and shutting it. 



3. Center the image of the field iris either 



a. On the Ortho-Illuminator by using (Fig. 42) the two screws lying 

 just in front of the field iris, or 



b. On a detached lamp by adjusting with the mirror and, when 

 necessary, moving the lamp. 



The objective, the field iris (which is presumed to be centered on the 

 field condenser ) , and the substage iris ( which is presumed to be centered 

 on the substage condenser) are now in line. It now remains to get the 

 illuminant onto the same optical axis. 



Centering the Light Source 



1. Make sure that the image of the field iris is still in focus. 



2. Replace one of the oculars with a pinhole ocular (Fig. 43). This 

 device is most conveniently screwed to one of the clamp screws of the 

 Ortho-Illuminator but must be purchased separately if another light 

 source is used. On the Ortho-Illuminator the color selector must be set 

 to zero and the intensity to maximum. 



3. Open both the field iris and the substage iris. 



4. Peep gingerly into the pinhole. If, as is almost certain, the glare 

 is blinding, either slip a neutral density filter into the system or cut 

 down the light emission with a rheostat. 



5. The eye will now see a sharp image of the lamp filaments. Center 

 these either 



a. On the Ortho-Illuminator by moving (Fig. 44) the two screws 

 at the back of the lamp housing, or 



b. On a separate lamp by moving the lamp, tilting the lamp, and 

 adjusting the mirror. This will probably throw the field iris out 

 of line, as can instantly be seen by looking into the other barrel 

 of the microscope, which still carries a normal ocular. It is now 

 necessary, looking in each barrel alternately, to tilt the lamp, 

 move the mirror, and move the lamp, until both field iris and 

 illuminant are centered. This infuriating procedure is what has 

 caused most microscopists to abandon separate lamps. 



