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& 
precision of 2 microns reading contact exposures. As a nicety, and to conform 
to the practical situation, exposures are made through cleared film base on 
the emulsion surface of spectroscopic plates, critical contact being maintained 
for all surfaces. 
Auto collimator - Verticality Device 
One important item of information that has been lacking to photogrammetrists 
and, with the advent of analytical triangulation is more than ever needed, is 
the knowledge of the precise attitude of the camera in space at the instant 
film is exposed. This information is now available in the AN/USQ-28 by 
virtue of the optical linkage between the KC-6A camera, whose attitude is 
determined by the characteristics of the camera mount, and the precision 
vertical. The optical linkage consists of a precision auto collimator totally 
within the KC-6A, except for the optical flat which is mounted on the inertial 
platform. Orientation of the camera as referenced by this optical axis 
(which in turn, is referenced by the Principal Point of Autocollimation) is 
thereby compared with the inertial platform. 
For each exposure, light is radiated from the flash package and illuminates 
a reticle etched on the black surface of a cube beam-splitter. A collimating 
objective then directs the light through the optical relay system to the inertial 
platform where it is reflected by an optical flat, rigidly mounted on that 
controlled system. The return beam is split by a beam-splitter such that 
half of the energy forms an image at a second sawtooth pattern reticle. A 
relay lens magnifies and re-images the reticles on film in the focal plane of 
the camera. 
The final presentation on film is shown in Figure 5. The sawtooth represents 
the attitude of the prime vertical, and the cross-hair represents the camera 
axis. Since the half pitch of the sawtooth is equivalent to 5-second displace 
ment of the camera axis with respect to the precision vertical, the displacement 
can be directly calculated. The autocollimator is aligned to the optical axis 
of the Geocon IV lens during calibration of the lens cone assembly, the parallel 
beam from the autocollimator being directed such that its axis is perpendicular 
to the focal plane as determined by the 3-lapped focal plane seating pads. 
Automatic Exposure Control 
The AEC system is designed to provide correct exposure over a terrain 
brightness range of 50 to 4000 foot lamberts with an ASA film rating range of 
20 to 2000 while accommodating filter factors of 1 and 2. Exposure is controlled 
by means of variable shutter speeds and apertures using a differential servo 
mechanism which maintains the shutter speed at a maximum. The effective