The Use of the Microscope 



29 



5 



Figs. 31, 32, 33, and 34. Setting up a medical microscope (continued). Fig. 31. The 

 field iris is closed. Fig. 32. The substage condenser is used to focus the image of the 

 field iris in the same plane as the object on the stage. Figs. 33 and 34. The eyepiece 

 is removed and the substage iris closed until it is seen just to cut off the edges of the 

 back lens of the objective. 



6. (Figs. 33 and 34.) Remove the eyepiece and look down the tube 

 from about 4 in. away. Close the substage iris— which has been wide 

 open since step 2— until it cuts off from one-tenth to one-fifth of the field. 

 The objective will now be working at a desirable 80 to 90 per cent of its 

 maximum aperture. 



7. Shuffle the neutral density filters until the desired intensity of illu- 

 mination is obtained. 



Steps 1 to 4 do not have to be repeated until either the lamp or micro- 

 scope is moved. Microscopes with an illuminant built into the stand 

 never require these adjustments to be made. Steps 5, 6, and 7 must be 

 repeated every time either the objective or the slide is changed. Each ob- 

 jective works at a different N.A. and has a different field of view. The 

 former must be adjusted with the substage iris and the latter with the 



