The coefficients K,,ı, Kası,... needed in (15) can be obtained from known 
distortion functions for object planes at distances s, ,s, by substituting s' for s in 
equation (12). 
camera axis 
0 
  
image plane for lens focussed 
on object plane at distance s 
  
O 
[aie 
—— oe 
ór, s r 
observed radial distance 
Q' P' in plane O O' 
| 
  
  
  
  
  
  
= 
Org r' 
observed radial distance 
in plane O' 
. image plane for lens focussed 
on object plane at distance s' 
Figure 1. Illustrating geometric relationship between Org and ôr, st - 
VARIATION BETWEEN NEAR AND FAR FIELD LIMITS OF PHOTOGRAPHIC FIELD 
In some close range applications one may well be required to measure points 
spanning the near and far limits of the photographic field. The extremities of the 
field according to standard depth of field formulas (Cox, 1956) are defined by the 
relations 
sy = near field limit = fs(1 + ) 
f+ Us 
(17) 
far field limit = = ) 
, 
in which s is the distance for which the camera is focussed and where 
LU = CN/f,