* * 
ar * 
} * 
fa 
= = 
A. > 
3 
respect to the camera axis, the maximum residual error at the corners of a wide-angle 
photograph (tan 45°=1) will equal the radial error, i.e. = 3 micron. Average error over 
the whole field will keep within 2 micron. 
The cams are by no means expensive. The user may provide himself with the lathe 
and construct the pair of cams corresponding to the objective he is using. 
  
Fig. 2 
For normal works the same pair of cams can be used for all the pictures taken by 
different lenses of the same type. 
The correcting device has always proved satisfactory in providing compensation of 
distortion even for objectives that are mostly affected by it, such as the wide-angle types 
derived from the Zeiss Topogon. 
It is however in connection with modern objectives which show little distortion values 
that the Santoni corrector operates at its best. 
In fact, as accuracy requirements have been increasing in surveys, it is impossible to 
renounce to correct the distortion still existing in these objectives, if only to the extent 
of a few hundreds of millimeter. 
On the other hand, although keeping within rather close limits, the distortion curves 
show a tendency to take on a trend far more individual than that appearing in objectives 
of older type, in which small individual aberrations were, perhaps, more easily disguised. 
Now, while a true reproduction of such individual curves represents no difficulty for the 
cam correcting device, I do not know whether such a thing may be said of either the 
optical-mechanical or the optical projection. 
Furthermore, it is not to be excluded that, if required, it would be possible to con- 
struct the cams so as to take care of small asymmetries that might exist between the 
two branches of the distortion curve for the same objective, and for different sections 
crossing its axis. 
This would obviously afford much better results in plotting than are obtained at 
present by the use of the so called “calibrated principal point". 
Finally, still keeping within the potentialities of future developments of mechanical