USEFUL TO THE MICROSCOPIST I I 2 I 



Equi-convex more accurately : 



Spherical 1 aberration 



In an equi-convex lens when /* = 1 516 



8/ = - 1-618 ....... . . . (xii 



To find the radius of either an equi-convex or equi-concave lens. 

 generally, the ref. index and the focus B/ being given : 



.......... lix) 



To find the radius of an equi-convex lens, the ref. index, the thickness, 

 and the focus B / being given : 





Bi-convex and bi-concave, generally : 



E_/= . (xii 1 . 



Correction for thickness : 



Bi-concave t may be neglected B/=E/ practically. 



Bi-convex more accurately, and converging and diverging menisci : 



- 



When the light is travelling from right to left 



r t 

 v < (/j. 1) - + s } 

 A/'= L. _ (xiv) 



Spherical aberration : 



V- -?? -T---i^! ' ' "> 



Example : Let r = 2, s = - 3, * = 1, and /x = ^ ; then by (xivl 

 1 Heath's Geo/iteti icnl Of tics, 1887. 



4 c 



