CASSEORAIN REFLECTOR WITH CORRECTED FIELD. 53 



and these give for the system 0,,...O" a the schemes, liuilt up just as on the 

 previous page, 



{ + '330582, +1-3619341 f + '380671, + T361508] 



> and [n + Snl { } 



-'208333, + 2-166667 J [-'208547, +2'165477j 



of which the first is the same as we had before, supplying a verification of the 

 solution of the equations for B,, B',. 



Substitute these in the schemes O u ...O',, in place of the values already used; 

 [n] is, of course, unchanged, and we find for 



f + '140266, +3-457242"! 

 [n+*], I- 



[-198505, +2'236634 J 



Hence G has now the same value in lx>th schemes and it is unnecessary to make a 

 further trial or change of the reverser, but there remains an excess in K of 55 

 units ; to deal with this, try reducing the curvature of each face of the second lens of 

 the corrector by one-hundredth part. This will give the schemes 



1, "1 fl, +-015000"! f 1, 



-'001254, + '657895 J\* 1 J \-r343976, + T520000_ 



+ '999981, + '009868] 



-1-345856, + '986738 J 

 and 



1, 1 fl, + -015000] f 1, 



-'001279, + '651381 J \* 



+ -999981, + -009771"] 



[n + Sn]. 

 -T385200, + '986484 J 



Substituting these in the combination O,,...O' S we get 



f + -140265, +3-457414") f + '140266, +3'457242] 



[J, -j > and [n + Sn], 4 



-'196543, +2-284718J [-'196543, +2'284996j 



(27) 



Hence both G and K are now identical, and, in consequence, both schemes indicate 

 the same principal focus and the same focal length ; in other words, complete 

 achromatism at the principal focus. 



5000"! f 1, * 1 



1 J [-1-383262, + 1-535200 J 



