(iy (2-p) 8r… / 
-]3 
Os ,s, T l-u E (2-p) ór. . 
By virtue of (22) these relations may be put in the alternative form 
[1 +7 
It is of interest to consider the ratios 
(Or p. bry s )/Örg , 
= (rss, = Org )/ Oe, 
which relate the total variation in distortion between near and far fields to the 
distortion at mid-field and infinity, respectively. Evaluating (26) by means of 
(24) and (25), we get 
28.  (q-1)-p) 
Os s ' 
p*q-2 
  
20 [aly 
Ps,œ AE [ES (2-p) 
1 =p? Log 
From the insight provided by the above results we may draw a number of 
inferences. First we note that for objects at low magnification (q» f) 
Pa, = 20-pu, (28)