INFRA-RED AND ULTRA-VIOLET MICROSCOPY 



235 



K. P. Norris and M. H. F. Wilkins devised a solid objective, 

 applicable to ultra-violet photomicrography, consisting of 3 quartz 

 elements linked together by optical contact (Fig. 9.10). Two of these 

 elements are aluminized at M and w; the occlusion ratio equates 35 



Fjg. 9.10. Norris and Wilkins solid reflecting objective. 



per cent. The N.A. 090 is achieved using water as immersion 

 medium. Bouwers and Blaisse have also developed an ultra-violet 

 solid objective (Fig. 9.11). The element (1) is aluminized in the 

 area m, which acts as a convex mirror and is surrounded by a small 



Fig. 9.11. Bouwers and Blaisse solid reflecting objective. 



semi-aluminized annular zone. The rays passing through the semi- 

 aluminized area are reflected on the completely aluminized area m. 

 In this way the occlusion ratio is reduced to 0-30. 



Lastly the '•ultrafluar" refracting objectives, developed by Zeiss, 

 should be referred to. These objectives are corrected in the 2300 

 to 7000 A range and provide very satisfactory imagery. They are 

 eminently suitable for ultra-violet microscopy and available in three 

 types : 



Ultrafluar x 32 77 sin w = 0-40 

 X 100 72 sin w = 0-85 

 X 100 77 sin w = 1-25 



