36 
Table 4 
Type of Methods Employed, 
1• Physicalische Technische Bundesanstalt, Braunschweig, 
West Germany. 
An edge scanning technique utilizing a scanning drum with 
appropriate electronic processing was employed to yield the 
MTF. The collimator focal length was 600 cm and the estimated 
accuracy was approximately J>% of the MTF at zero spatial fre 
quency. 
2. Royal Aircraft Establishment, Farnborough, Bngland. 
A spread function line scanning technique was employed. 
Subsequent fourier analysis by computer programs yielded the 
OTF. The estimated accuracy was ± of the MTF at zero spat 
ial frequency. 
3* British Broadcasting Corporation 
A sinusoidal variable-density target was employed. Gne 
fixed spatial frequency target, located in the image plane was 
made to effectively represent a variable spatial frequency by 
changing its orientation with respect to the field slit placed 
immediately in front of the sinusoidal target. Measurements 
of the separate sine and cosine transmission components are there 
by made at different spatial frequencies. Computation of the 
OTF is subsequently carried out (given by the root of the sum 
of the squares of these two components)• A 305 cm focal length 
collimator was employed. The estimated accuracy was -2% of 
the MTF at zero spatial frequency. 
Institute of Optical Research, Stockholm, Sweden. 
A spread function line scanning technique was employed. 
Subsequent Fourier analysis by computer programs yielded the 
OTF. The estimated accuracy was about 5% of the MTF at zero 
spatial frequency. 
3» British Scientific Instrument Association. 
A square wave (crenelate-type) pattern was used. A fixed 
single spatial frequency target was located in the object plane 
on a rotating disc. Variation of the effective spatial frequency 
was accomplished by changing the line target orientation with 
respect to a field slit. Continuous scanning and appropriate 
electronic filtering is used to yield the OTF directly. The 
collimator had a focal length of 120 cm. The estimated accuracy 
was -0.5^ of the MTF at zero spatial frequency.