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e* 
The question of IMC in a mapping camera has always aroused considerable 
discussion. It is admittedly an advantage in obtaining maximum image quality 
of which the optical system is capable. On the other hand, the possible loss 
of knowledge of the inner orientation elements due to film motion during 
exposure makes the technique suspect to photogrammetrists. 
If instantaneous exposures were possible, it is obvious that no such problem 
would exist. However, mapping cameras are limited in effective exposure 
speeds due to the between-the-lens shutter requirements and the need for 
lens apertures small enough to correct distortion of wide angle systems. 
Compared to a panoramic camera, for instance, which utilizes speeds of 
1/500/second to 1/4000/second, the mapping camera will generally range 
from 1 / 300/second to 1 / 800/second. Image Motion Compensation is 
therefore more likely to be needed in mapping cameras than in the newer 
reconnaissance types. 
The answer to the problem lies in precisely locating the Principal Point of 
Autocollimation at the center of exposure time for each shutter speed. If, 
for instance, the fastest IMC speed of the KC-6A - 0. 8"/second is used in 
conjunction with a 1/ 100 second shutter speed, a total motion of 0. 0080" 
takes place during exposure. This represents a possible 200 microns of 
uncertainty, a figure which rejects photogrammetric precision. Figure 6, 
however, graphically shows the timing whereby the excellent geometric 
characteristics of the KC-6A will be maintained while using IMC. All motions 
and lamps which illuminate fiducials, or the verticality readouts, are timed 
from the receipt of the initiate pulse. The shutter ready pulse to the syn 
chronizer is set at 200 milliseconds after start. The 1/100 second exposure 
occurs between 210 and 220. Secondary fiducial recording occurs at the 
opening of the shutter, 210 milliseconds. Primary fiducials, vertical readout, 
and the freeze pulse for the cathode ray tube display and distance measurement 
equipment, occur always at the mid-cycle of the shutter opening time; in 
this case at 215 milliseconds. Timing is therefore precise to a millisecond 
for geometric control. 
Of second importance is the duration of the exciting time of the lamps. Both 
primary and secondary fiducial lamps have a duration of 1 millisecond. 
Verticality readout lamps are 400 microseconds in duration; freeze pulse is 
8 microseconds. It can therefore be seen that the Principal Point of Auto 
collimation can be located with an error not exceeding 10 microns under an 
extreme condition. This important complex of functions is tested during 
the calibration phase to assure the operational photogrammetric capability 
of the camera. 
Figure 7 shows the focal plane of the assembled cone. The three focal plane 
blocks and the moving guides which support the platen during IMC can be seen 
on the tip of the cone.