240 



HANDBOOK OF PHOTOGRAPHY 



group A. If the sky is slightly cloudy an exposure of Ko sec. at //16 is required. 

 But, since the permissible shutter speed is Hoo sec, we shall have to increase the 

 aperture to obtain correct exposure at J^oo sec. If we are using a film having a speed 



Table XVI. — Exposure for Outdoor Photography at Night 

 (Weston Ratings— 10 to 20) 



Subject 



Shop fronts, brightly lighted 



Illuminated grounds, or buildings 

 with interior illumination 



Open street scenes, without near 

 dark objects 



Open street scenes, without dark 

 near objects, snow-covered 

 ground or wet pavements 



Street scenes with near dark objects 



Street scenes with near dark ob- 

 jects, snow-covered ground or 

 wet pavement 



Buildings with floodlight illumina- 

 tion only 



Floodlighted open street scenes 

 without near dark objects 



FloodUghted street scenes, with 

 near dark objects 



Aperture 



//2 //2.8 //4.0 //5.6 //8 //ll //16 //22 //32 



Exposure time 



4 s 



8s 



15 s 



10 s 

 30 s 



20 s 

 30 s 



1 m 



2 m 



15 m 



30 m 



1 h 



40 m 

 2h 



IMh 

 2h 

 4h 

 8h 



Table XVI gives suggested exposures for various subjects for outdoor night photography. The 

 wide range of conditions which are actually encountered requires that Table XVI be used as a guide in 

 determining suitable exposures, rather than to provide fixed and unvarying data. 



1. Film Speed. — Table XVI is based on a film speed having a tungsten rating of Weston 10 to 20. 

 For converting the given exposures with films having other speeds, 



multiply exposure time by 16 for speeds between 0.6 and 1.2 



2. Aperture. — Table XVI shows exposures for nine apertures. For converting to other apertures, 

 see Eq. (23). 



of Weston 20 for which Table VIII applies, we can then determine the requisite aper- 

 ture by using the expression 



Thus the correct aperture for our example will be 



• = 16\/M^ = 6.2 (48) 



An aperture of //6.3 would be correct. 



