-16- 
This lens design is approaching the ultimate in the Geocon 
series in theory. Its on-axis resolution approaches 300 lines per 
millimeter, i. e. diffraction limited. Distortion of all forms is 
theoretically about one micron and in practice is less than 8 microns. 
If a combination of wide angle, color correction, resolution, and dis 
tortion are considered collectively, it is anticipated that the Geocon 
IV is about the ultimate in a 6-inch lens which can be produced at any 
reasonable cost. 
The Airborne Digital Computer is an integral part of the navi 
gation subsystem. It collects and compiles all navigational and sup 
porting information necessary for accurate surveying, mapping, 
control and steering of the aircraft. One of its outputs feeds directly 
into the digital recorder. This recorder tape can be fed directly into 
the ground data handling system for rapid checking of mission per 
formance and then for the precise calculations required to orient and^ 
position the aerial photography. 
The computer is a hybrid digital machine incorporating both 
general purpose and special purpose computing sections. The logic 
grouping is in three basic divisions: General purpose computer 
(GP); two digital differential analyzers (DDA); and input-output (10) 
communication buffer, sections. Memory for the computer is pro 
vided by a contact-head magnetic storage drum with a 8448 word 
capacity. 
The general purpose section functions as the controller of the 
computer. It is a binary, serial accessed machine using a one-plus- 
one address instruction word format which specifies the operand 
track, operand sector, next instruction sector, and the instruction 
code. The general purpose section is capable of performing serial 
arithmetic operations, logical decisions, and controlling the DDA 
and thè input-output buffers.