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= + 3-434 

 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 conden-t-i . 



Thickness AB=-683. 



Working distance B0='317. 



Diameter of the plane surface 1> of front lens=l'192, AO=1'0, 

 AV=1-51. 



The angle 2=62. and < = :>o : 47'; the numerical aperture of 

 the combination is therefore 1'33 X.A. 



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



V- 

 next two DC. FE only amounts to - -'214 J -. The back correcting 



