238 



PROGRESS IN MICROSCOPY 



The visible-light source So can be imaged on the slit K by means of 

 the lens Lo. Since the microscope is focused in white light, it requires 

 no change in the ultra-violet. 



Burch's objective, at O, is used minus the eyepiece, thus eliminating 

 its aberrations. With an objective of N.A. 0-65 and a tube length 

 of 345 millimetres, the image projected direct on the photographic 

 plate at E is magnified x 110. 



Fig. 9.14. Diagram of the Burch microscope for photomicrography in visible and ultra- 

 violet light. 



As in infra-red, transposing an ultra-violet image in visible light 

 is feasible. To convert into colour variations the absorption variations 

 of an object investigated in ultra-violet light, Brumberg devised an 

 ingenious method; he makes three exposures of the object at three 

 different ultra-violet wave-lengths. Next, these three negatives are 

 projected and superimposed on a screen through three differently 

 coloured filters. The colour variations evince the absorption variations. 

 The Polaroid Corporation has devised an apparatus, built on this 

 principle, that promptly provides a coloured image. 



Image converters are also used in the ultra-violet. Figure 9.15 

 shows the Bausch and Lomb ultra-violet microscope to which an R.C.A. 

 converter is fitted. 



