Another measure of stability of the KC-1B which was investigated was the relation of the PS to the 
PPA. Since this distance (a vector actually) is affected by asymmetric distances of off-axis images, 
the tipping and curvature of the calibration plates on which the images are recorded can change the 
values. Figure 6 lists the values for the PPA and the PS distance from the PPA. The average distance 
is then obtained from all calibrations on each camera and also the maximum variance. This maximum 
variance is then used to judge stability of geometry. Figure 7 shows that only one camera has an 
extreme value. The remaining twelve cameras show maximum variances not exceeding eight micrometers. 
This very sensitive indicator implies high geometric stability. 
TANGENTIAL DISTORTION 
Tangential distortion maximum is shown in the last column of Figure 6 for each calibration. When 
the values are five micrometers maximum or less, the Planigon lens can be considered well aligned and 
mounted free of strain. Larger values, however, should be suspect and subject to investigation because 
for this lens (at least) external forces affecting the lens mount can increase the tangential distor- 
tion (ten to thirty-five micrometers have been experienced). These have not been due to lens manu- 
facturing errors but to external forces on the lens, and have been corrected when found during cali- 
bration. It can be said for the KC-1B that the low values of tangential distortion are another proof | 
of stability of lens-camera geometry. | 
CALIBRATED FOCAL LENGTH (CFL) 
The final gemoetric data which has been examined in this study is the calibrated focal length. 
Figure 6 lists the value for each calibration and the differences are readily apparent. The range of 
values for three cameras are large: 27, 36, and 57 micrometers. The two largest differences occur 
when Fairchild and Hill A.F.B. certificates are comapred. It is significant to note, however, that 
calibrations occurred eleven and thirteen years apart. Furthermore, no record exists as to whether 
the lens cones in these cameras received major repair. The remaining ten cameras show differences in 
CFL which do not exceed twenty micrometers. 
The use of the CFL as an indicator of geometric stability may be questionable since certificates 
quote probable errors of ten and twenty micrometers. It becomes another question which users should 
answer. 
SUMMARY 
Stability of the KC-1B, as judged from recorded geometry of calibrations, appears to be of a high 
order in consideration of the facts of military handling and periodic complete overhaul and repair. 
Some of the cameras were first calibrated as far back as 1959 at the manufacturer's camera calibration | 
laboratory and their data compared favorably with that of the Hill Air Force Base certificates; tests | 
being ten to thirteen years later. The fundamental fact is that these are data from routine E nnd 
calibrations. No special emphasis nor technique was used in any case and no records were kept of | 
repairs that could affect geometric values. The study has been informative but does raise the question 
of what stability is essential to the company or mapping agency doing the most accurate mapping. 
85 
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