68 



PHOTOMICROGRAPHY 



There is also much less reflection at the lens surface when 

 the light passes through oil. 



The Effect of Oil Immersion on Numerical Aperture. 



lens of objective 



Immersion Fluid 

 Cover-glass 



Object Slide 



Condenser 



Mounting Med 



Immersion Fl 



Fig. 21 



COMPARISON OF OIL-IMMERSION AND DRY SYSTEMS 



The aperture of the objective and its light-gathering 

 power depend on the obliquity of the rays which can 

 enter it. In the diagram OK represents the extreme ray. 

 The effect of the condenser on the illumination of the 

 object and on the N.A. of the objective will be considered 



