110 



INSTRUMENTATION 



5. Open the iris diaphragm of the lamp so that approximately the entire field of 

 view of the microscope can be observed. The procedure that follows this depends 

 on the type of substage condenser unit. If both the substage condenser and the 

 condenser diaphragm are separately centerable with respect to the optical axis of 

 the microscope, then the next step is to align the optical axis of the substage condenser 

 with the optical axis of the objective and, following that, to adjust the condenser 

 diaphragm so that the image of the annular opening is centered upon the conjugate 

 area of the diffraction plate. If the substage condenser has been precentered, it is 

 necessary only to center the condenser diaphragm. In order to make either or 



Fig. III. 4. Centering the substage condenser and diaphragm for phase micros- 

 copy, (a) The substage condenser is decentered with respect to the optical axis of 

 the microscope, (b) The substage condenser is centered with respect to the optical 

 axis of the microscope, (c) The phase diaphragm is decentered with respect to a 

 diffraction plate of the type TA + 5. {d) The phase diaphragm is centered with 

 respect to a diffraction plate of the type TA + 5. (e) The phase diaphragm is de- 

 centered with respect to a diiTraction plate of the type TB + d. (/) The phase 

 diaphragm is centered with respect to a diffraction plate of the type TB + S. 



both of these adjustments, replace the eyepiece of the microscope by the centering 

 telescope and focus the telescope on the coating of the diffraction plate. If the 

 substage condenser is to be centered, remove the diaphragm which has been inserted 

 for use with the diffraction plate and close the iris diaphragm on the substage con- 

 denser mount until it appears in the field of the centering telescope. If the optical 

 axis of the condenser is not in alignment, the image of the iris diaphragm appears 

 decentered as in Fig. III. 4a. Turn the proper centering screws until the iris dia- 

 phragm appears centered as in Fig. III.46. For final use of the phase microscope, 

 open the iris diaphragm until the entire conjugate area of the diffraction plate is 

 visible. Replace the condenser diaphragm for the phase objective and manipulate 

 the centering adjustments for the diaphragm until the image of the opening is 

 centered upon the conjugate area. Figure III. 4c shows the appearance of the image 



