FRANgON'S SYSTEM FOR PHASE MICROSCOPY 



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8. FRANGON'S SYSTEM FOR PHASE MICROSCOPY 



Frangon (1950) devised a means for applying the method of phase 

 microscopy without modifying the optical elements of the ordinary 

 microscope. An intermediate image that is stigmatic and aplanatic is 

 formed at unit magnification between the object specimen and the 

 microscope objective. The optical assembly that forms the inter- 

 mediate image contains the diffraction plate or its equivalent, and the 

 ordinary microscope produces a magnified image of the intermediate 



Frangon's hemisphere 



Microscope 

 objective 



To eyepiece' 

 Conjugate area 



Complementary area 



Fig. III. 12. Schematic drawing of Franc^on's hemisphere for producing a phase 



contrast image. 



phase contrast image. The numerical aperture of the microscope ob- 

 jective may be as high as 1.30. 



The device proposed by Frangon is placed between the specimen and 

 the microscope objective. Figure III. 12 illustrates this device and 

 the manner in which the phase contrast image is formed. In Fig. III. 12, 

 BCDE represents the surface of a segment of a glass hemisphere cut 

 into two parts along the plane MGN parallel to the base AOF of the 

 hemisphere so that the distance OG is equal to one-half the radius of 

 curvature of the hemisphere. is the center of curvature of the 

 hemisphere. The two surfaces which result from the cut along MGN 

 are polished. The central circular area KL of the surface at MGN of 

 the upper part of the hemisphere is opaque. A dielectric film having a 



