PHASE VERTICAL-ILLUMINATION MICROSCOPE 



149 



of the condensing lens system in the illuminator tube is variable, and 

 the inner and outer diameters of the conjugate area of the diffraction 

 plates contained in objectives of different power are made to a common 

 ratio. Thus the correct match between the image of the condenser 

 diaphragm and the conjugate area of the diffraction plate is produced 

 by varying the magnification of the image of the single condenser 

 diaphragm. Figure III. 10 is a photograph of the Cooke, Troughton 

 and Simms phase contrast incident-light microscope. This firm also 



Phase Regular 



observation observation 

 system system 



Projector j 

 system I 



4" 



'(^^^^ 



Removable 

 prism 



annulus 



Fig. III. 11. Layout of the Bausch and Lomb reflected-light microscope with phase 



contrast accessories. The phase accessories are shaded to differentiate them from 



the microscope proper. Courtesy of Bausch and Lomb Optical Co. 



supplies (1949) phase contrast equipment for the Vickers projection 

 microscope. The unit supporting the phase objective and the illumina- 

 tor tube is attached to the instrument by means of a bayonet joint and 

 is interchangeable with the universal illuminator. The phase objectives 

 are achromatic objectives of a standard series of numerical apertures 

 and powers and are adjusted for work with no cover glass at a tube length 

 of 250 mm. Each objective is supplied with a beam splitter, a dif- 

 fraction plate, and a magnetic centering mount. 



The Bausch and Lomb Optical Co. has adopted the scheme reported 

 by Benford and Seidenberg (1950). This system is illustrated in Fig. 

 III. 11. Advantage is taken of the fact that the size of the image of the 

 condenser diaphragm (the clear annulus of Fig. III. 11 is the condenser 

 diaphragm) produced at the back focal plane of the objective remains 

 substantially the same regardless of the focal length of the objective. 

 The diffraction plate is placed at the exit pupil of the projector system. 

 The same diffraction plate can be retained with the objectives of dif- 

 ferent power, and then only one condenser diaphragm is required. The 



