PHASE-CONTRAST MICROSCOPY 



85 



and the objective Oi, is collected by the projection-eyepiece L that 

 images it at S[\ on the phase-plate Q. The image /*', of the specimen P, 

 is collected by L which forms an image /*", after being reflected on Q. 

 This is the image perceived in the eyepiece O.. The phase-plate Q 



Fig. 2.21. The Frangon-Nomarski device (Nachet). 



consists of a glass plate whose face against which the light impinges 

 is flat, well polished and coated with a metal layer evaporated in vacuo. 

 Provision is made to remove metal in slit-shaped area of width ab. 

 In Fig. 2.21 this slit lies lengthwise at right angles to the plane of the 

 figure. The diaphragm ^i is a slit, too, its image S[' being overspread 

 by ab. Thus the direct light is reflected on to the glass at ab while 



