EXPOSURE AND EXPOSURE DEVICES 229 



raphers, for professional photographers should certainly be able to determine exposure 

 correctly, even without any aids, more than 45 per cent of the time. 



Economic Justification for Exposure Meters. — If we adopt Milbauer's figures as 

 given in Table VI, it is possible to arrive at some conclusions regarding the economic 

 justification of photographic exposure aids. 



Table VI. — Correct Exposure Obtained with Various Exposure Aids 



Percentage of 

 Exposure Device Correct Exposures 



Exposure tables 45 . 



Slide-rule devices, circular calculators, etc 47 . 2 



Visual-type exposure meters, carefully used 87 . 8 



Photoelectric exposure meters 97 . 3 



By discarding exposure tables for exposure calculators of the slide-rule or disk 

 type, it is possible to increase the number of properly exposed negatives from 45 to 

 47.2 per cent, a gain of 2.7 per cent. If a visual type of instrument is employed, the 

 gain in correct exposures jumps from 45 to 87.8 per cent, representing an increase of 

 32.8 per cent. Good visual-type exposure meters are available in the United States 

 for less than $3, and if their use assures that an additional 33 per cent of the negatives 

 which are taken will be properly exposed, the meter will have paid for itself by the 

 time $10 worth of film has been exposed. 



On the basis just outlined, the use of a photoelectric exposure meter cannot be 

 economically justified so easily because of the greater expense of these meters and the 

 fact that the maximum possible improvement remaining is only 12.2 per cent. But 

 the use of a photoelectric exposure meter will enable 52.3 per cent more films to be 

 correctly exposed than exposure tables, and 10.5 per cent more than are correctly 

 exposed with visual exposure meters. If $20 is assumed to be the price for a photo- 

 electric exposure meter and that it will give an additional 52.3 per cent of correctly 

 exposed film than exposure tables, it will take a film expenditure of $40 to pay for the 

 meter. The 12.2 per cent improvement of the photoelectric type over the visual type 

 of meter is attained with an expenditure for the meter of an additional $17. The sum 

 will be amortized by a 12.2 per cent increase in properly exposed negatives after $139 

 worth of films have been exposed. 



But an exposure meter merits consideration aside from the purely monetary aspect. 

 The picture is the final result that is desired, and one picture may well be worth the 

 cost of the meter in aesthetic value to the maker or commercially on the photographic 

 market. 



Exposure Devices. Use of Exposure Tables. — Undoubtedly the best method avail- 

 able for determining the proper exposure of photographic materials under most condi- 

 tions (and for most branches of photography) is the proper use of the photoelectric type 

 of exposure meter. Although the prices of these units have been reduced considerably 

 in the past few years, they are still relatively expensive and are beyond the means of 

 some photographers. In such cases recourse may be made to visual exposure meters 

 or to exposure tables or calculators. 



Reasonably extensive exposure tables are included in this chapter as an aid to 

 the determination of the correct exposure. Such tables must be used with judicious 

 discretion, and their use does not assure that proper exposure will always be attained. 

 They can give only approximate exposure values which, on the basis of experience, 

 have proved satisfactory for the conditions to which they apply. Unusual conditions 

 encountered in practical photography may frequently require that the photographer 

 deviate somewhat from the exposures indicates in the tables. 



