132 



PROGRESS IN MICROSCOPY 



nelled spectrum between polarizers. Five or six channels are adequate. 

 The device then lets through some higher-order white light. The plate 

 is half-wave but not for a single wave-length only: it applies to a whole 

 series of wave-lengths distributed within the spectrum. The device is 



Fig. 4.5. The light reflected by the object P re-appears with the aid of a quarter-wave 



plate Q. 



Fig. 4.6. Carbon observed with a standard objective (G. Nomarski). 



truly achromatic. Figures 4.5 and 4.6 show the same object, observed 

 with an illuminator of the type shown in Fig. 4.1, with and without 

 quartz plate (Fig. 4.7). 



Considerable advances have been made, not only from the stray- 

 light standpoint, important problem in reflected-light microscopy, but 



