SUBJECTIVE SHARPNESS OF IMAGES 



577 



mensions used In the main experiments, will show that the magnifica- 

 tion was reduced from 12 to 9.3, the area of the external aperture was 

 increased from 0.49 square inch to 1.00 square inch, and the aperture 

 was mounted 2.6 inches instead of 1.3 inches from the principal planes 

 of the projection lens. 



LENS 



^ V PLANES j APERTURE 



U 



36" 

 72.3 



Fig. 7 — Essential dimensions of the motion picture optical system as used for the 

 subjective sharpness tests. For this case a^ = 0.49 square inch. 



36 X 



723 ■ 72.3 + X 



1.88 y. 



The television apparatus was designed for 240 lines, 24 frames per 

 second, and a width : height ratio of 7 : 6. Actually 20 per cent of the 

 frame time was consumed in scanning the blank space between sound 

 film frames, and 10 per cent of the line time was used up by the return 

 sweep in the receiver. The television image, which was the same size 

 as the projected motion picture, was 5.6 inches high. This dimension 

 was 20 per cent less than the height of the entire 240-line field including 

 the blank portion, which was, therefore, 6.9 inches. The width of the 

 entire field including return trace was 6.9 X 7/6 or 8.1 inches, and the 

 width of the television image was 10 per cent less than this, or 7.3 

 inches. Thus, the total area transmitted per frame period was 

 6.9 X 8.1 or 56 square inches; the useful image area was 5.6 X 7.3 or 

 41 square inches. 



The three amplitude-frequency characteristics used in the video 

 circuit are shown in Fig. 8. Curve A is for two square scanning 

 apertures in tandem, one transmitting and one receiving, each having 

 the height of one scanning line. No electrical band limitation was 

 effective in this case. Curves B and C are for the addition of each of 

 two special low-pass filters which were carefully phase-equalized and 



