582 



BELL SYSTEM TECHNICAL JOURNAL 



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Z 5.5 



O 5.0 



- 4.5 



Z 



o 



«5 4.0 



3.0 



7^ 2.5 



2.0 



Fit 



5 10 15 20 25 30 35 40 45 50 55 60 65 70 



LENS DISPLACEMENT IN SCALE DIVISIONS 



9 — Calibration curve for the motion picture optical system as used for the 

 subjective sharpness tests. 



of the lens from its sharp focus position. The lens displacement is 

 expressed in microscope scale divisions, the working variable. Figure 

 7 shows the dimensions of the optical system. 



2. Equipment and Conditions of the Experiment 

 Light Source 

 A ground glass screen 3^ inch behind the film, illuminated by a 1,000- 

 watt projection lamp and double condensing lens system. This served 



