Focal plane 

 of eyepiece 



Rear focal plane 

 of objective 



Objective 



Microscope stage 



Condenser 



Figure 11-12. Diagram Illustrating the Optical Path of Deviated and 

 Undeviated Light Through the Ordinary Light Microscope. 



transmitted by the object will tend to cancel each other out (destructive 

 interference) and make the object darker than its surroundings (Figure 

 11-13). This is dark or positive phase-contrast (Figure 11-14 (a)). 



Bright or negative phase-contrast, in which the object appears brighter 

 than its surroundings, is obtained by retarding the undeviated light by Va 

 wavelength at the diffraction plate (conjugate area). Since the deviated 

 light has already been retarded by V4 wavelength at the object, the 



230 / CHAPTER 11 



