SUBSTAGE CONDENSERS AND CONDENSER MOUNTS 119 



included. A special phase condenser, N.A. 0.9, is supplied in a non- 

 centering mount. 



In other makes of substage condenser mounts which have a revolvable 

 changer plate for the condenser diaphragms, the entire plate is moved 

 when any one of the diaphragms is centered. Rotating a second dia- 

 phragm into place below the condenser may require recentering of the 

 changer disk. Several photographs were made available to illustrate 

 this type of turret substage mount. Figure III. 5. 3 is a photograph of a 

 Bausch and Lomb microscope stand fitted with phase objectives and 

 with a substage condenser mount having a rotatable changer. The 

 condenser is an Abbe type, N.A. 1.25, and fits into a non-centering 

 mount. Figure III. 5. 4 shows the Cooke, Troughton and Simms phase 

 microscope and the auxiliary centering telescope. A condenser with 

 N.A. 1.0 is available for slides of standard thickness. I. Koristka and 

 Co. (Fig. III. 5. 5) also supplies such a rotatable changer disk on the 

 substage condenser mount of its phase contrast "universal" model 

 microscope. The condenser may be obtained in either a centering or a 

 non-centering mount. Koristka and Co. includes in this turret' mount a 

 means for passing gradually from phase contrast illumination to central 

 conical illumination in each phase objective. (The method for ac- 

 complishing this has been described by Kohler and Loos, 1941. Three 

 polarizing elements are used. One element contains an annular opening 

 free of polarizing material. A second element has a central, clear 

 aperture, the diameter of which is smaller than the inner diameter of 

 the annular opening in the first element. These two elements of 

 polarizing material are crossed and are mounted together in the rotatable 

 disk. A third uniform polarizing element is mounted below the con- 

 denser and can be rotated through 90°. It is so oriented that at one 

 extreme position light passes to the condenser only through the central 

 aperture and such that at the other extreme position light is admitted 

 only through the annular aperture.) Figure III. 5. 6 is a photograph 

 of the Reichert phase microscope with a turret substage mount. The 

 numerical aperture of the condenser is 0.95. The auxiliary centering 

 telescope is also shown. Figure III. 5. 7 shows the substage condenser 

 mount with changer disk for diaphragms on the Zeiss-Winkel phase 



Fig. III.5.2. (a) Top view of Wild substage condenser mount with rotatable 

 changer plate for diaphragms, (b) Bottom view of Wild substage condenser mount 

 with rotatable changer plate for diaphragms, (c) Wild phase contrast accessories 

 on stand listed as a research and routine microscope for medical purposes. Cour- 

 tesy of Henry W^ild Surveying Instruments Supply Co., Ltd. (1949). 



