EXPOSURE AND EXPOSURE DEVICES 



235 



Table XI gives the exposure data for photofiood lamps, having various types of 

 reflectors, for various distances between lamp and the subject. The table is devised 

 for only one photofiood lamp; if two, three, or four lamps are used in the same reflector, 

 the exposure times may be reduced to one-half, one-third, or one-fourth of the time 

 specified for the single lamp. 



Table XI. — ^Table of Basic Exposure for Black-and-white Still Photography 



Using Photoflood Lamp 

 (Weston Ratings— 10 to 20) 



Table XI gives the recommended exposures for subjects lighted by photoflood lamps of various 

 sizes and for different distances between the lamp and the subject. 



1. Film Speed. — Table XI is based on the use of film having a tungsten speed rating of Weston 

 10 to 20. For other film speeds the exposure time required is inversely proportional to the Weston 

 rating. 



2. Aperture. — Exposures for four standard apertures are given. For converting data of Table XI 

 for other apertures, see Eq. (23). 



3. Number of Lamps. — Only one lamp of the type specified is assumed. If n similar lamps are 

 used at the same distance from the subject, divide the exposure times by n. It should be noted that 

 two No. 1 lamps are equivalent to one No. 2 lamps, and two No. 2 lamps are equivalent to one No. 4 

 photoflood lamp. 



