108 



PHOTOMICROGRAPHY 



of achromatic and aplanatic condensers for critical work 

 is now so generally recognised that quite a large series 

 of corrected condensers is made, among which is the Abbe 

 achromatic condenser of N.A. 1-0. It has a focal length 

 of J", and an aplanatic aperture of 0-65 ; with front lens 

 removed its power is reduced to I" and its aplanatic cone 

 to 0-3. 



Aplanatic and Achromatic Substage Condensers are made 

 of the following types : 



All the above condensers should have an aplanatic 

 cone nearly as great as their N.A. ; that of the condensers 

 of N.A. 1-0, for instance, is usually about 0-9 or 0-95. 



Fig. 34 



LOW-rOWEU ILLUMINATOR BY SWIFT 



Fig. 35 



ACHROMATIC CONDENSER, WATSON *S "UNIVERSAL" 



