146 



INSTRUMENTATION 



formed an image, Di, of the diaphragm below the specularly reflecting 

 surface of the object specimen. The light was reflected by the surface 

 of the specimen and passed through the objective again to form a real 

 image, D2, of the diaphragm. Image Do became the exit pupil and 

 therefore the location of the dift'raction plate. In one trial, the optical 



To eyepiece 



Diffraction plate c 



/ 



Objective 



3-—D, 



Condenser diaphragm D 



\-< — >- 



I 



I 



D2-^-<A^^ "^Field lens \ 



f^ — ---J Field st:p 



, Specularly reflecting specimen 



Light 

 source 



Fig. III. 9. Optical system of the experimental phase contrast vertical-illumination 



microscope designed by Jupnik et al. 



system was adjusted to form image D2 below the beam splitter (broken 

 lines), and in a second experiment image D2 was formed above the beam 

 splitter (solid lines). Locating the exit pupil between the beam splitter 

 and the eyepiece, as in the second arrangement, minimized both the 

 amount of stray light and losses of illumination. The dift'raction plate 

 for the phase vertical illuminator was a glass plate coated in the same 

 way as the dift'raction plate used in an objective for observing a trans- 

 mitting specimen. Cuckow (1949) used a phase objective designed for 

 transmission work to show that the phase vertical illuminator is a very 

 useful tool in metallurgy. Taylor (1949) compressed the optical as- 

 sembly consisting of the microscope objective lenses, the beam splitter, 

 and the diffraction plate into the objective mount. The beam splitter 

 was placed immediately above the lenses of the objective, and the image 

 of the condenser diaphragm was formed on the diffraction plate located 

 above the beam splitter. 



