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HANDBOOK OF PHOTOGRAPHY 



Table XII shows basic exposure data for ordinary incandescent lamps operated at 

 normal voltages which result in a lamp life of approximately 1000 hr. The use of 

 clear or frosted lamps, rather than blue "daylight" lamps, is assumed. The table is 

 calculated for a lamp having a power-consumption rating of 100 watts, but the correct 

 exposure for lamps of other power rating TT' may be determined by multiplying by 

 100/W. The table applies to portraits and light-colored interiors. For darker 

 subject matter the exposures should be increased; exposure should be decreased for 

 lighter than average subjects. 



Table XIII gives the proper aperture when photo flash lamps are used at a specified 

 distance from the subject. The table is based on the assumption that the shutter will 

 be opened throughout the duration of the flash; if synchronized flashes are used, one 

 stop larger than is indicated should be used. 



Exposure data for flashlight powders is given in Table XIV, although photoflash 

 lamps have almost entirely superseded the use of flashlight powders. The table gives 

 the basic amount of flashlight or magnesium powder suitable for use with a film having 

 a speed or sensitivity rating of Weston 24 to 48. 



Table XIV. — Exposure with Flashlight Powders 

 (Weston Ratings— 24 to 48) 



The tables are based on film sensitivity of Weston 24 to 48. For other speeds, 

 multiply apertures by 6 for Weston speeds between . 6 and 



4 



2.5 



1.4 



1 



0.6 



1.5 



4 

 10 

 24 

 64 



1.2 

 3.5 



20 



48 



128 



The method of calculating exposure through the use of closing the diaphragm until 

 the detail which it is desired to record just disappears may be explained as follows: 

 Cover the camera and head with focusing cloth, and focus the subject at the full lens 

 aperture. After the eyes have been accustomed to the luminous intensity of the 

 ground-glass screen, stop down the lens aperture slowly until the detail in the deepest 

 shadow it is desired to record has just disappeared. Detail in the deepest shadow 

 would be faintly, but distinctly, observable when the eyes are directly opposite that 

 portion of the ground glass on which the shadows occur. Note this aperture stop 



