5 
Light from the flying spot scanner which is reflected by the pellicle 
is focused by a 9-inch focal length f/11 lens at a 1:1 magnification 
ratio upon a raster centering mask. Light passing through the 
openings of the mask is collected by a condensing lens which images 
the raster on a photomultiplier tube. 
The raster scan pattern consists of 320 interlaced TV lines in 
the manual mode. At maximum raster size the dimensions of the pattern 
is 80 x 80 mm. The scan pattern can be nominally varied on the face 
of the scanner from 80 mm to 8 mm giving a 10X electronic zoom capa 
bility. Thus the scan size, through the 16X optical train, on the 
diapositive is varied from 5 mm to 0.5 mm. 
The raster, by its nature, obtains more information in the 
direction of the lines than in the direction of scan. Therefore to 
obtain balanced error information from the correlation circuitry in 
both the x and y direction the scan pattern is electronically switched 
through 90°. The function of the correlation system is to locate 
the conjugate imagery being scanned on the tables to a high degree 
of accuracy. The signals from each photomultiplier tube are processed 
in order to correlate on the most useful and valid information. For 
this comparator system a multiplying type of correlation is used. 
Delay lines are used to give the servo system intelligence to more 
the measuring table to the point of maximum correlation. By corre 
lating on the signals from diapositive A and the delayed signal from 
diapositive B, and vice versa, information is gained on the direction 
in which parallax is decreasing or increasing. By inputting this 
information to a servo motor, the motor drives the table in the 
decreasing parallax direction and conjugate imagery is obtained. 
RESULTS 
As of this writing, a detailed evaluation of the performance of 
the equipment has not been performed. Sufficient data have been 
obtained, however, to make definitive statements concerning system 
performance. Tests have been performed during a preliminary acceptance 
test and many times during the test and adjust phase of the development. 
The tests that have been performed are on the accuracy and short 
term stability of the instrument in the manual mode, repeatability 
accuracy in the automatic mode, and accuracy of marking. Both aerial 
photographic diapositives and photocopy grid plates have been used.