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ADJUSTMENT OF THE NINE-LENS AERIAL CAMERA OF THE 
U.S. COAST AND GEODETIC SURVEY 
G. C. Tewinkel. 
The U.S. Coast and Geodetic Survey has been successful in compiling topo 
graphic maps of standard accuracy using a nine-lens aerial camera with consid 
erable economic advantage over contemporary single-lens methods. The com 
plete nine-lens system includes four principal instruments: the aerial camera, a 
transforming printer, a rectifying camera and special stereoscopic plotting 
apparatus. This paper describes the adjustment of the mirrors and lenses of the 
camera, whereas Mr. Harris discusses the calibration of the photographs and 
the efficiency of the stereoscopic plotting in the proceedings of Commission II. 
The nine lenses are arranged with all their axes vertical and parallel, and 
with eight of the lenses forming a regular octagon around the center one. All 
the lenses are normal-angle Ross Xpres, f = 21 cm. Light rays from the ground 
vertically beneath the camera enter the center lens in the usual manner, and 
the film area is masked to form a large octagon. Marginal rays, however, cannot 
enter the center lens, but are deflected upward through the outer lenses by 
means of steel mirrors 15 X 25 cm. The inclination of each mirror is 19° from 
the vertical, creating an equivalent oblique image having a tilt of 38°. The nine 
separate areas are arranged over the same piece of negative film which is 58 X 
58 cm. 45 fiducial marks, a clock and numbering device are also shown on the 
negative film, with 41 of the marks appearing in the margins of the image 
area. These marks are a graphic record of fixed positions in the aerial camera, 
and are used later as guides in the transformation procedure to correct for 
film distortion and camera calibration field tests. An overlap of about 5 mm in 
the image area around each segment allows a uniform junction of images on 
the finished print. No negative image is farther than 9 cm from a fiducial mark. 
The transformed photograph is a composite nearvertical 90 X 90 cm, 
f = 21 cm, printed on a single piece of photographic paper. The total angular 
coverage of the complete photograph is 135° at the sides and 143° at the 
corners. 41 of the fiducial marks appear on the finished print: one in the 
center, 24 near the perifery of the center octagon, and 16 along the outer 
edges. These fiducial marks are made to fit predetermined templet positions 
in the photographic laboratory. 
Each mirror is fastened to a steel “cone” with nine steel adjusting screws. 
The cone is fastened permanently to a lens plate. Each lens is set in a steel 
mounting, which in turn is held to the lens plate by steel adjusting screws. 
The metal of the mirrors, the cone, lens plate, lens mountings, and of all the 
bolts and nuts is from the same ingot of a special stainless steel that has a 
stable coefficient of thermal expansion. Thus, there is no tendency for the 
relative orientation of the mirrors and lenses to change because of thermal 
differences. Moreover, the nuts are all painted with shellac as an added 
precaution against their accidental slipping. A mirror is removed and resurfaced 
about once every two years because of mechanical erosion of the reflecting 
surface while the mirror is in the slip stream of the airplane during aerial 
photography.