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The camera user appreciates the possibility provided for varying the system. ' This includes, for .: ^s 
example, one-man to three-man survey flights, the use of the camera either singly or as part of a > 1 
dual system etc. With a modern system, both single and serial photographs should be possible without 
the need for any changes to be made to the system configuration. 
Finally, the possibility of extending the basic system of the camera must also be required. It should 
be easily possible to extend the standard aerial camera by additional components, such as an automatic 
exposure control, recording on each exposure the camera data and data of external instruments, etc. 
The term external instruments should include inertial navigation systems, Doppler systems, VLF 
systems and recording systems in general. 
The cost of a set of aerial photographs is affected to only a very small degree by the amount of 
depreciation chargeable for the camera. The costs of the aircraft, staff and control-point marking 
accounts for far the greater part of the total cost. The high total cost requires that every mission 
flown should be completely successful. This assurance can be achieved only if the complete photo- 
graphic system is reliable, including the photographic equipment and aircraft on the one hand and 
the pilot, operating and laboratory staff on the other. 
The theory of reliability clearly shows that possibilities exist for increasing the safeguards against | 
failure. However, systems with very high MTBF values (mean time between failures) all for redundant 
systems which would increase by several times the cost of an aerial camera. Thus, provision must be 
made in awareness of the limits of cost-effectiveness to prevent operating errors and instrument 
defects or breakdowns. Examples for frequently occurring operating mistakes are badly plugged-in 
connecting cables, too high or too low a supply voltage, incorrect polarity of the supply voltage, an 
inadequate vacuum due to dirty systems etc. To prevent breakdowns within the camera itself, it is 
essential to provide circuits throughout to ensure that the modules and components used are perfectly 
protected against excessive voltage, power surges or thermal overloads. 
Apart from preventive measures as regards operating mistakes and camera defects, the requisite aids 
must be provided for the operator and servicing specialist, in order to simplify maintenance, servicing 
and repairs of the camera system. These must include programs and facilities for a rapid diagnosis. 
A modular system will then make it possible to replace components and sub-assemblies in a minimum of 
time. 
The criterion regarding the reliability of a survey flight, to which reference was made at the 
beginning, means in practice that under no circumstances must any exposure be missing. Thus, an 
optimum camera should enable the operator to decide on the basis of detailed information provided to 
him on defects, whether the flight should be continued or abandoned, despite the presence of an 
operating error or an instrument defect. 
2. TECHNOLOGY OF THE 1980s: THE MICROCOMPUTER 
  
The pocket calculator that is now commonly used is very similar to a microcomputer. It is thus very s e | 
suitable for explaining the basic principles of the microcomputer. |. A pocket calculator has the = Han li 
following components: 
- input in the form of a keyboard 
- internal computer unit i 
- output unit in the form of a display 
- control unit 
Pocket calculators can be used only to solve arithmetical problems. For this reason, a digital . | 
method is the most obvious. In order to represent-a-decimal number, four binary data are required. M 
The accuracy of the mathematical operation depends on the number of binary places used in this 
operation. Figure 1 shows the basic principle of the pocket calculator. 
  
  
CONTROL UNIT 
  
  
  
  
  
  
  
  
  
INPUT a OUTPUT 
ARD Y 
KEYBO UNIT DISPLA 
  
  
  
  
  
  
  
  
  
Fig 1: Block Diagram of a Pocket Calculator 
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