(235) 
procedure based on field calibration photographs. 
The residual number of interference lines across the working area of a 
mirror can always be reduced to less than 10 which corresponds to about 
3 microns. The effect of this lack of flatness on image definition is indiscernible: 
no difference in image definition can be detected along the junction between 
the wing chambers (which use mirrors) and the center chamber (which has 
no mirror) where the image scales are equal on the negative. 
A chart of the collimator cross errors and a map of the residual interfer 
ence fringes are recorded both before and after a season’s operation of the 
camera. Even though the camera is subjected to the intense heat while parking 
on airfields in Florida, the intense cold of high altitudes in Alaska, and the 
mechanical shock of many airplane landings, yet the discrepancies are only one 
or two lines of interference. Thus the relative orientation of the nine lenses, 
eight mirrors and 45 fiducial marks is not disturbed by aerial photographic 
operations. 
The advantages of double and triple camera mapping systems has long 
been recognized. The nine-lens camera has an ultra-wide angular field in both 
the direction of flight and perpendicular to it; the precise inner orientation is 
maintained with certainty. Thus the camera is a powerful surveying tool, 
which is particularly economical where geodetic control is sparse. 
References. 
Reading, O. S., The Nine-Lens Camera of the Coast and Geodetic Survey, 
Photogrammetric Engineering. 
, vol. 1, No. 5, pp. 6—13, 1935. 
, vol. 4, No. 3, pp. 184—192, 1938. 
Tewinkel, G. C., The Reading Plotter, Photogrammetric Engineering, vol. 
XIII, No. 2, June 1947. 
Tewinkel, G. C., The Reading Plotter, Photogrammetric Engineering, vol. XV, 
No. 3, September 1949. 
Swanson, L. W., Topographic Manual Part II Photogrammetry, U.S. Govern 
ment Printing Office, 1949; p. 67 ff, 225, 445 ff. 
Tewinkel, G. C., Adjustment of the Nine-Lens Camera, The Journal of the 
Coast and Geodetic Survey, U.S. Department of Commerce, No. 
3, April 1950, p. 45