188 



THE TECHNICS OF PHASE MICROSCOPY 



good negatives on the high-speed black and white emulsions. Photo- 

 micrographs have been made at 1800 X with all contrasts of the Spencer 

 oil immersion phase objectives with loadings of 2 to 2.5 kv and 75 to 

 120 /if (150 to 250 watt-seconds). The exposure duration was esti- 

 mated to be about 1/35,000 second by Mr. Frank Carlson (General 

 Electric Co.), to whom Richards is grateful for assistance and equip- 

 ment. The flash tubes and power packs are available commercially, and 

 lens systems can be combined to illuminate the microscope. By adding 

 a timing circuit to the timelapse motion picture equipment an elec- 

 tronic flash could be used although, as Carlson points out, the resulting 



(-n 



Fig. IV.5. Diagram for electronic flash illumination for photomicrography. A, 

 focusing light. B, FT-230 flash tube. C, condensing system. D, microscope. E, 

 image of focusing lamp filament and flash tube electrodes on underside of the micro- 

 scope condenser. 



pictures may be so sharp as to appear jerky on projection. (Figures 

 V.IP, V.IQ, MAF, YAH, VIA, and VI. 6 were made by electronic flash.) 



Film for the phase microscope is chosen according to the criteria 

 established for any other kind of photography. A process or positive 

 type of emulsion is suitable when the specimen is uncolored and there is 

 enough light. Richards favors a fine-grained type B panchromatic 

 film for general use such as Panatomic X or its equivalent, and develops 

 in DK-50 by time and temperature. Others will get eciually good 

 results with other materials and procedures. When color is important 

 the emulsion suitable must be sensitive enough to record the color 

 directly or to give a correct rendering in black and white. Cole (1949) 

 reports increased contrast with a Polaroid filter. 



With Spencer phase equipment, Richards (19476) found that the 

 IB— 0.25X diffraction plate did not require increased exposure. The 

 0.2A±0.25X low-contrast diffraction plates usually took about the same 

 exposure as required by brightfield microscopy with the condenser 

 closed enough to give best contrast on the ground glass. The higher 



