29 
Appendix 4. 
Inter-Laboratory Test: Comparative Measurements of Lens CTF 
The comparison of MTF measurements described in this 
Appendix was carried out with the support of the Avionics 
Laboratory, Reconnaissance Division, Wright Air Development 
Centre, United States Air Force, under Contract AF 33 (657) 
-9156. Acknowledgeris made of permission to use the 
results of this experiement, also of the co-operation of the 
participating laboratories. Several other laboratories 
generously offered to make their facilities available, but 
time prevented acceptance. 
The Reconnaissance Division, WADC, provided a 12 inch 
focal length, f/4 Covogon lens (Serial No. 102, F.D. 10.926, 
manufactured by the General Scientific Corporation). A pro 
gram was developed to send this lens to a number of different 
laboratories. Itek was then to collate all the data obtained 
and compare the results from different laboratories, the object 
being to provide positive evidence of the degree of accuracy 
that might be expected in the measurement techniques. The test 
specifications are reproduced in Table 1 of this appendix. 
Representative measurements from eight different labor 
atories were obtained. The test conditions (angular field, 
focal position, line orientation, and spectral conditions) 
for which curves were obtained are summarized in Tables 2 and 
3. A list of the participants is given in Table 4 together 
with an indication of the particular techniques employed.* 
Details of each of the methods (where published) will be found 
in the references given. Tests in a narrow (monochromatic) 
spectral bandwidth located at 546nm wavelength and also for a 
wide spectral bandwidth were carried out. The narrow band peak 
transmission wavelength and bandwidths are tabulated in Table 
5* The broad band spectral conditions are indicated in Figure 
6. The curves in full lines are those indicated by the labor 
atory concerned. The dashed lines were estimated (at Itek) to 
correspond to the spectral conditions used (and were not spec 
ifically given by the test laboratory). Due to time limitations, 
and to the need to make measurements without resetting up dis 
mantled or modified equipment, it was not possible for all the 
laboratories to carry out tests to cover all the conditions 
originally specified. For these or other reasons no single 
laboratory, in fact, submitted a complete set of data as tab 
ulated in Tables 2 and 3 (this was not drawn up until the data 
was finally collated). It was also necessary to ’process” some 
of the data received since the data was not always provided in 
the most suitable form for the present comparison. This was 
necessary to ensure that the curves were referenced to the best 
focus curve (on axis) at 40 cycles/mm. Thus for both the narrow 
* Different techniques may have been adopted since this 
report was written.