USEFUL TO THE MICROSCOPIST II2I 



Equi-convex more accurately : 



Spherical l aberration 



8 f= -^""J^y y f ( xi ) 



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



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

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



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

 and the focus B / being given : 



2/i 

 Bi-convex and bi-concave, generally : 



/LI 1 s-r 

 Correction for thickness : 





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



Bi-convex more accurately, and converging and diverging menisci 



8 

 B/- 



When the light is travelling from right to left 

 r/fc-i)*+ t \ 



A/= lr_^ L^ ...... (xiv> 



( M - l)|r--0* -1)-} 

 Spherical aberration : 



o 



Example : Let r = 2, s = - 3, t = 1, and /z = ; then by (xiv) 

 1 Heath's Geometrical Optics, 1887. 



4c 



