IMMERSION FRONT FOR CONDENSER BY NELSON 367 



the dispersive power is 64*0, the chromatic aberration of the triplet 

 is very small. Moreover the glass is hard and perfectly safe to use. 



Radii : curve A= + -602 



B = 00 



C =-f3-434 



D= + 1-280 ' 

 E= 15-078 

 F= + 2-359 

 Diameters : lens FE=2'45 



DC=2-1 



Distance between surfaces : ED ='05 



CA=-03 



FIG. 320. Nelson's new immersion front for a condenser. 



Thickness AB=-683. 



Working distance BO=-317. 



Diameter of the plane surface B of front lens= 1*192, AO=1'0, 

 AY=1-51. 



The angle c = 62, and <=35 47'; the numerical aperture of 

 the combination is therefore 1*33 X.A. 



The front lens AB is aplanatic ; the spherical aberration of the 



yi 



next two DC. FE only amounts to '214 "~. The back correcting 



