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Microscopy /29 : 5 



of the specimen. At sharp changes of the refractive index, such as at 

 the edge of the nucleus, light beams coming through the nucleus and 

 through the surrounding cytoplasm interfere in the image to produce a 

 halo. The interference-contrast microscope is a similar variation of the 



Microscope Objective 



Fully Silvered 



Reflector, R 



Immersion Oil 



Cemented Interface 

 Plate, U 



Slide 



Fully Silvered Spot, F 

 Light from Condenser 



Figure 7. Dyson's interference contrast microscope. Both 

 the object and the fully silvered spot F are focused with unit 

 magnification on the opening V at the vertex of the spherical 

 reflector R. Basically, the light is split into two beams at the 

 upper surface of L which is half-silvered. The reference beam 

 goes from the upper surface of L down to F and then back to V. 

 The object beam goes from the upper surface of L through the 

 object and thence to V. Both surfaces of plate V are half- 

 silvered. The phase screw moves the slightly wedge-shaped 

 plate L, thereby allowing the adjustment of the phase of the 

 reference beam. 



ordinary microscope in which the final image represents the inter- 

 ference of two (or more) beams of light. One beam is transmitted 

 directly through the specimen. The interference-contrast microscope 

 differs from the phase-contrast microscope in that the second beam 

 comes through a very different part of the object. This avoids the halo 

 formation at the edge of the nucleus and similar artifacts. 



One form of the interference-contrast microscope is illustrated in 

 Figure 7 and another in Figure 8. In the first form, one external beam 

 is combined with the transmitted beam to give an interference pattern. 



